Monday, 7 September 2015
Botany First Year Chapter 5 Q&A sample
1. Why is homology helpful in identifying the organisms? (02) marks
ANSWER
In the context of biology, homology is the existence of shared ancestry between a pair of
structures, or genes, in different species. A common example of homologous structures in
evolutionary biology is the wings of bats and the arms of primates. Evolutionary theory explains
the existence of homologous structures adapted to different purposes as the result of descent
with modification from a common ancestor. For instance, the forelimb of a bear, the wing of a
bird, and your arm have the same functional types of bones as did our shared reptilian ancestor.
Therefore, these bones are homologous structures. The more homologies two organisms possess,
the more likely it is that they have a close genetic relationship.
2. What does bio-chemistry provide the field of biology? (02) marks
ANSWER
Biochemistry, sometimes called biological chemistry, is the study of chemical processes within and
relating to living organisms. By controlling information flow through biochemical signaling and the
flow of chemical energy through metabolism, biochemical processes give rise to the complexity of
life. Much of biochemistry deals with the structures, functions and interactions of biological
macromolecules, such as proteins, nucleic acids, carbohydrates and lipids, which provide the
structure of cells and perform many of the functions associated with life.
3. Is genetics really definitive in identifying organisms? (02) marks
ANSWER
Genetic analysis is the overall process of studying and researching in fields of science that involve
genetics and molecular biology. DNA sequencing is essential to the applications of genetic
analysis. This process is used to determine the order of nucleotide bases. Each molecule of DNA is
made from adenine, guanine, cytosine and thymine, which determine what function the genes
will possess. By generating a DNA sequence for a particular organism, you are determining the
patterns that make up genetic traits and in some cases behaviors. The advent of DNA sequencing
has significantly accelerated biological research and discovery.
4. Briefly state the 5 kingdom scheme by Robert Whittaker. (02) marks
ANSWER
All living things were lumped together into two kingdoms, namely plants and animals. Animals
included every living thing that moved, ate, and grew to a certain size and stopped growing. Plants
included every living thing that did not move or eat and that continued to grow throughout life. It
became very difficult to group some living things into one or the other, so early in the past century
the two kingdoms were expanded into five kingdoms: Protista (the single-celled eukaryotes);
Fungi (fungus and related organisms); Plantae (the plants); Animalia (the animals); Monera (the
prokaryotes).
5. How was the 5 kingdom scheme by Robert Whittaker modified by Marguilis and Schwartz? (02) marks
ANSWER
Bacteria were included in plants. Many biologists found this system satisfactory, while others
found it unworkable for many unicellular organisms like euglena that have both plant like
(presence of chlorophyll) and animal like (lack of cell wall) characters and also because it ignores
the difference between prokaryotic and eukaryotic cells. In 1866 Ernst Hackel proposed a third
kingdom Protista to accommodate euglena like organisms and bacteria.
Lynn margulis and karlene Schwartz (1988) modified five kingdom classification of whittaker by
considering cellular organization, mode of nutrition, cytology, genetics and organelles of symbiotic
origin (mitochondria, chloroplast). These five kingdoms are prodaryotae (monera), protoctista
(protists), plantae, animalia and fungi.
6. What is a virus and how is it classified? (02) marks
ANSWER
A virus is a small infectious agent that replicates only inside the living cells of other organisms.
Viruses can infect all types of life forms, from animals and plants to microorganisms, including
bacteria and archaea. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen
infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in
1898, about 5,000 virus species have been described in detail, although there are millions of
different types.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type,
mode of replication, host organisms, and the type of disease they cause.
7. Explain in detail the animal diseases caused by viruses. (07) marks
ANSWER
The viruses of vertebrates are informally distinguished between those that primarily cause
infections of humans and those that infect other animals. The two fields of study are called
medical (or clinical) virology and veterinary virology respectively. Although not the first viruses to
be discovered and characterised, those that cause infections of humans are the most studied.
Different viruses can infect all the organs and tissues of the body and the outcomes range from
mild or no symptoms, to life-threatening diseases. Humans cannot be infected by plant or insect
viruses, but they are susceptible to infections with viruses from other vertebrates. These are
called viral zoonoses or zoonotic infections. Examples include, rabies, yellow fever and pappataci
fever.
Marine mammals are susceptible to viral infections. In 1988 and 2002, thousands of harbor seals
were killed in Europe by the measles-like phocine distemper virus. Large outbreaks of the disease
were recorded among the seal populations of Lake Baikal and along the shores of the Baltic and
North Sea. The infection resembled canine distemper; the animals died within two weeks of
respiratory distress and many aborted pups were seen. Many other viruses, including caliciviruses,
herpesviruses, adenoviruses and parvoviruses, circulate in marine mammal populations.
Measles, also known as morbilli, rubeola, or red measles, is a highly contagious infection caused
by the measles virus. Initial signs and symptoms typically include fever, often greater than 40 °C
(104.0 °F), cough, runny nose, and red eyes. Two or three days after the start of symptoms, small
white spots may form inside the mouth, known as Koplik's spots.
Mumps, also known as epidemic parotitis, is a viral disease caused by the mumps virus. Initial
signs and symptoms often include fever, muscle pain, headache, and feeling tired. This is then
usually followed by painful swelling of one or both parotid glands. Symptoms typically occur 16 to
18 days after exposure and resolve after 7 to 10 days. Symptoms in adults are often more severe
than in children. About a third of people have mild or no symptoms. Complications may include
infections of the coverings of the brain (15%), pancreatitis (4%), permanent deafness, and painful
testicular swelling which uncommonly results in infertility.
Rubella, also known as German measles or three-day measles, is an infection caused by the
rubella virus. This disease is often mild with half of people not realizing that they are sick. A rash
may start around two weeks after exposure and last for three days. It usually starts on the face
and spreads to the rest of the body. The rash is not as bright as that of measles and is sometimes
itchy. Swollen lymph nodes are common and may last a few weeks. A fever, sore throat, and
fatigue may also occur. In adults joint pain is common. Complications may include bleeding
problems, testicular swelling, and inflammation of nerves. Infection during early pregnancy may
result in a child born with congenital rubella syndrome (CRS) or miscarriage.
9. Write a short note on hepatitis. (02) marks
ANSWER
Viral hepatitis, including hepatitis A, hepatitis B, and hepatitis C, are distinct diseases that affect
the liver and have different hepatitis symptoms and treatments. Other causes of hepatitis include
recreational drugs and prescription medications. Hepatitis type is determined by laboratory tests.
A person can spread the hepatitis A virus about a week before his or her symptoms appear and
during the first week of having symptoms. People with no symptoms can also spread the virus.
Hepatitis B is a virus that infects the liver. Most adults who get it have it for a short time and then
get better. This is called acute hepatitis B. Sometimes the virus causes a long-term infection, called
chronic hepatitis B. Over time, it can damage your liver. Babies and young children infected with
the virus are more likely to get chronic hepatitis B. This infection of the liver is caused by the
hepatitis C virus. About 3.2 million people in the U.S. have the disease. But it causes few
symptoms, so most of them don't know.
10. Explain in detail human disease with emphasis on HIV-AIDS. (07) marks
ANSWER
AIDS is the more advanced stage of HIV infection. When the immune system CD4 cells drop to a very low level, a
person's ability to fight infection is lost. In addition, there are several conditions that occur in people with HIV infection
with this degree of immune system failure -- these are called AIDS-defining illnesses. A person gets HIV when an
infected person's body fluids (blood, semen, fluids from the vagina or breast milk) enter his or her bloodstream. The
virus can enter the blood through linings in the mouth, anus, or sex organs (the penis and vagina), or through broken
skin. Both men and women can spread HIV. A person with HIV can feel normal, and still give the virus to others.
Pregnant women with HIV also can give the virus to their babies. Anyone can get HIV if they engage in certain activities.
You may have a higher risk of getting HIV if you:
· Have unprotected sex. This means vaginal or anal intercourse without a condom or oral sex without a latex
barrier with a person infected with HIV.
· Share needles to inject drugs or steroids with an infected person. The disease can also be transmitted by dirty
needles used to make a tattoo or in body piercing.
· Receive a blood transfusion from an infected person. This is very unlikely in the U.S. and Western Europe,
where all blood is tested for HIV infection.
· Are born to a mother with HIV infection. A baby can also get HIV from the breast milk of an infected woman.
The only way to know if you have HIV is to take an HIV test. Most tests looks for signs of HIV in your blood. A small
sample of blood is taken from your arm. The blood is sent to a lab and tested for HIV.
· Standard tests. These blood tests check for HIV antibodies. Your body makes antibodies in response to the HIV
infection. These tests can't detect HIV in the blood soon after infection because it takes time for your body to
make these antibodies. It generally takes two to 8 weeks for your body to produce antibodies, but in some
cases it can take up to six months.
· In standard tests, a small sample of your blood is drawn and sent to a lab for testing. Some of the standard
tests use urine or fluids that are collected from the mouth to screen for antibodies.
· Rapid antibody tests. Most of these are blood tests for HIV antibodies. Some can detect antibodies in saliva.
Results are available in under 30 minutes and are as accurate as standard tests.
· Antibody/antigen tests. These tests are recommended by the CDC and can detect HIV up to 20 days earlier
than standard tests. They check for HIV antigen, a part of the virus that shows up 2-4 weeks after infection.
These tests can also detect HIV antibodies. A positive result for the antigen allows treatment to begin earlier
and the patient to avoid infecting others. These are blood tests only. Rapid antibody/antigen test. One
antibody/antigen tests delivers results in 20 minutes.
· In-home test kits. These kits -- there are two available in the U.S. -- screen blood and saliva for HIV antibodies.
Signs that HIV is turning into AIDS include:
· A fever that won't go away
· Sweating while you sleep
· Feeling tired all the time (not from stress or lack of sleep)
· Feeling sick all the time
· Losing weight
· Swollen glands (neck, groin, or underarms)
· Oral thrush
We've come a long way from the days when diagnosis with HIV equaled a death sentence. Today, there are a variety of
treatments that, when used in combination can significantly slow down and in some cases stop altogether, the
progression of HIV infection. After HIV infection is confirmed, your doctor will start you on a drug regimen consisting of
several drugs; combinations of different types of anti-HIV drugs sometimes are called HAART, for highly-active
antiretroviral therapy (HIV is a kind of virus called a retrovirus). Taking HAART therapy is very manageable yet isn’t
necessarily easy. These drugs must be taken at the right time, every single day. Also, a range of side effects may occur,
including: diarrhea, nausea, rash, vivid dreams, or abnormal distribution of body fat. And, especially if medications are
taken incorrectly or inconsistently, the virus can mutate, or change, into a strain resistant to treatment. The good news
is that there are now several HIV medications that are only taken once a day. If there is resistant virus, however, these
may not work and other medication options must be used. If your disease has progressed to AIDS, your treatment may
also include drugs to combat and prevent certain infections.
ANSWER
In the context of biology, homology is the existence of shared ancestry between a pair of
structures, or genes, in different species. A common example of homologous structures in
evolutionary biology is the wings of bats and the arms of primates. Evolutionary theory explains
the existence of homologous structures adapted to different purposes as the result of descent
with modification from a common ancestor. For instance, the forelimb of a bear, the wing of a
bird, and your arm have the same functional types of bones as did our shared reptilian ancestor.
Therefore, these bones are homologous structures. The more homologies two organisms possess,
the more likely it is that they have a close genetic relationship.
2. What does bio-chemistry provide the field of biology? (02) marks
ANSWER
Biochemistry, sometimes called biological chemistry, is the study of chemical processes within and
relating to living organisms. By controlling information flow through biochemical signaling and the
flow of chemical energy through metabolism, biochemical processes give rise to the complexity of
life. Much of biochemistry deals with the structures, functions and interactions of biological
macromolecules, such as proteins, nucleic acids, carbohydrates and lipids, which provide the
structure of cells and perform many of the functions associated with life.
3. Is genetics really definitive in identifying organisms? (02) marks
ANSWER
Genetic analysis is the overall process of studying and researching in fields of science that involve
genetics and molecular biology. DNA sequencing is essential to the applications of genetic
analysis. This process is used to determine the order of nucleotide bases. Each molecule of DNA is
made from adenine, guanine, cytosine and thymine, which determine what function the genes
will possess. By generating a DNA sequence for a particular organism, you are determining the
patterns that make up genetic traits and in some cases behaviors. The advent of DNA sequencing
has significantly accelerated biological research and discovery.
4. Briefly state the 5 kingdom scheme by Robert Whittaker. (02) marks
ANSWER
All living things were lumped together into two kingdoms, namely plants and animals. Animals
included every living thing that moved, ate, and grew to a certain size and stopped growing. Plants
included every living thing that did not move or eat and that continued to grow throughout life. It
became very difficult to group some living things into one or the other, so early in the past century
the two kingdoms were expanded into five kingdoms: Protista (the single-celled eukaryotes);
Fungi (fungus and related organisms); Plantae (the plants); Animalia (the animals); Monera (the
prokaryotes).
5. How was the 5 kingdom scheme by Robert Whittaker modified by Marguilis and Schwartz? (02) marks
ANSWER
Bacteria were included in plants. Many biologists found this system satisfactory, while others
found it unworkable for many unicellular organisms like euglena that have both plant like
(presence of chlorophyll) and animal like (lack of cell wall) characters and also because it ignores
the difference between prokaryotic and eukaryotic cells. In 1866 Ernst Hackel proposed a third
kingdom Protista to accommodate euglena like organisms and bacteria.
Lynn margulis and karlene Schwartz (1988) modified five kingdom classification of whittaker by
considering cellular organization, mode of nutrition, cytology, genetics and organelles of symbiotic
origin (mitochondria, chloroplast). These five kingdoms are prodaryotae (monera), protoctista
(protists), plantae, animalia and fungi.
6. What is a virus and how is it classified? (02) marks
ANSWER
A virus is a small infectious agent that replicates only inside the living cells of other organisms.
Viruses can infect all types of life forms, from animals and plants to microorganisms, including
bacteria and archaea. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen
infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in
1898, about 5,000 virus species have been described in detail, although there are millions of
different types.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type,
mode of replication, host organisms, and the type of disease they cause.
7. Explain in detail the animal diseases caused by viruses. (07) marks
ANSWER
The viruses of vertebrates are informally distinguished between those that primarily cause
infections of humans and those that infect other animals. The two fields of study are called
medical (or clinical) virology and veterinary virology respectively. Although not the first viruses to
be discovered and characterised, those that cause infections of humans are the most studied.
Different viruses can infect all the organs and tissues of the body and the outcomes range from
mild or no symptoms, to life-threatening diseases. Humans cannot be infected by plant or insect
viruses, but they are susceptible to infections with viruses from other vertebrates. These are
called viral zoonoses or zoonotic infections. Examples include, rabies, yellow fever and pappataci
fever.
Marine mammals are susceptible to viral infections. In 1988 and 2002, thousands of harbor seals
were killed in Europe by the measles-like phocine distemper virus. Large outbreaks of the disease
were recorded among the seal populations of Lake Baikal and along the shores of the Baltic and
North Sea. The infection resembled canine distemper; the animals died within two weeks of
respiratory distress and many aborted pups were seen. Many other viruses, including caliciviruses,
herpesviruses, adenoviruses and parvoviruses, circulate in marine mammal populations.
Measles, also known as morbilli, rubeola, or red measles, is a highly contagious infection caused
by the measles virus. Initial signs and symptoms typically include fever, often greater than 40 °C
(104.0 °F), cough, runny nose, and red eyes. Two or three days after the start of symptoms, small
white spots may form inside the mouth, known as Koplik's spots.
Mumps, also known as epidemic parotitis, is a viral disease caused by the mumps virus. Initial
signs and symptoms often include fever, muscle pain, headache, and feeling tired. This is then
usually followed by painful swelling of one or both parotid glands. Symptoms typically occur 16 to
18 days after exposure and resolve after 7 to 10 days. Symptoms in adults are often more severe
than in children. About a third of people have mild or no symptoms. Complications may include
infections of the coverings of the brain (15%), pancreatitis (4%), permanent deafness, and painful
testicular swelling which uncommonly results in infertility.
Rubella, also known as German measles or three-day measles, is an infection caused by the
rubella virus. This disease is often mild with half of people not realizing that they are sick. A rash
may start around two weeks after exposure and last for three days. It usually starts on the face
and spreads to the rest of the body. The rash is not as bright as that of measles and is sometimes
itchy. Swollen lymph nodes are common and may last a few weeks. A fever, sore throat, and
fatigue may also occur. In adults joint pain is common. Complications may include bleeding
problems, testicular swelling, and inflammation of nerves. Infection during early pregnancy may
result in a child born with congenital rubella syndrome (CRS) or miscarriage.
9. Write a short note on hepatitis. (02) marks
ANSWER
Viral hepatitis, including hepatitis A, hepatitis B, and hepatitis C, are distinct diseases that affect
the liver and have different hepatitis symptoms and treatments. Other causes of hepatitis include
recreational drugs and prescription medications. Hepatitis type is determined by laboratory tests.
A person can spread the hepatitis A virus about a week before his or her symptoms appear and
during the first week of having symptoms. People with no symptoms can also spread the virus.
Hepatitis B is a virus that infects the liver. Most adults who get it have it for a short time and then
get better. This is called acute hepatitis B. Sometimes the virus causes a long-term infection, called
chronic hepatitis B. Over time, it can damage your liver. Babies and young children infected with
the virus are more likely to get chronic hepatitis B. This infection of the liver is caused by the
hepatitis C virus. About 3.2 million people in the U.S. have the disease. But it causes few
symptoms, so most of them don't know.
10. Explain in detail human disease with emphasis on HIV-AIDS. (07) marks
ANSWER
AIDS is the more advanced stage of HIV infection. When the immune system CD4 cells drop to a very low level, a
person's ability to fight infection is lost. In addition, there are several conditions that occur in people with HIV infection
with this degree of immune system failure -- these are called AIDS-defining illnesses. A person gets HIV when an
infected person's body fluids (blood, semen, fluids from the vagina or breast milk) enter his or her bloodstream. The
virus can enter the blood through linings in the mouth, anus, or sex organs (the penis and vagina), or through broken
skin. Both men and women can spread HIV. A person with HIV can feel normal, and still give the virus to others.
Pregnant women with HIV also can give the virus to their babies. Anyone can get HIV if they engage in certain activities.
You may have a higher risk of getting HIV if you:
· Have unprotected sex. This means vaginal or anal intercourse without a condom or oral sex without a latex
barrier with a person infected with HIV.
· Share needles to inject drugs or steroids with an infected person. The disease can also be transmitted by dirty
needles used to make a tattoo or in body piercing.
· Receive a blood transfusion from an infected person. This is very unlikely in the U.S. and Western Europe,
where all blood is tested for HIV infection.
· Are born to a mother with HIV infection. A baby can also get HIV from the breast milk of an infected woman.
The only way to know if you have HIV is to take an HIV test. Most tests looks for signs of HIV in your blood. A small
sample of blood is taken from your arm. The blood is sent to a lab and tested for HIV.
· Standard tests. These blood tests check for HIV antibodies. Your body makes antibodies in response to the HIV
infection. These tests can't detect HIV in the blood soon after infection because it takes time for your body to
make these antibodies. It generally takes two to 8 weeks for your body to produce antibodies, but in some
cases it can take up to six months.
· In standard tests, a small sample of your blood is drawn and sent to a lab for testing. Some of the standard
tests use urine or fluids that are collected from the mouth to screen for antibodies.
· Rapid antibody tests. Most of these are blood tests for HIV antibodies. Some can detect antibodies in saliva.
Results are available in under 30 minutes and are as accurate as standard tests.
· Antibody/antigen tests. These tests are recommended by the CDC and can detect HIV up to 20 days earlier
than standard tests. They check for HIV antigen, a part of the virus that shows up 2-4 weeks after infection.
These tests can also detect HIV antibodies. A positive result for the antigen allows treatment to begin earlier
and the patient to avoid infecting others. These are blood tests only. Rapid antibody/antigen test. One
antibody/antigen tests delivers results in 20 minutes.
· In-home test kits. These kits -- there are two available in the U.S. -- screen blood and saliva for HIV antibodies.
Signs that HIV is turning into AIDS include:
· A fever that won't go away
· Sweating while you sleep
· Feeling tired all the time (not from stress or lack of sleep)
· Feeling sick all the time
· Losing weight
· Swollen glands (neck, groin, or underarms)
· Oral thrush
We've come a long way from the days when diagnosis with HIV equaled a death sentence. Today, there are a variety of
treatments that, when used in combination can significantly slow down and in some cases stop altogether, the
progression of HIV infection. After HIV infection is confirmed, your doctor will start you on a drug regimen consisting of
several drugs; combinations of different types of anti-HIV drugs sometimes are called HAART, for highly-active
antiretroviral therapy (HIV is a kind of virus called a retrovirus). Taking HAART therapy is very manageable yet isn’t
necessarily easy. These drugs must be taken at the right time, every single day. Also, a range of side effects may occur,
including: diarrhea, nausea, rash, vivid dreams, or abnormal distribution of body fat. And, especially if medications are
taken incorrectly or inconsistently, the virus can mutate, or change, into a strain resistant to treatment. The good news
is that there are now several HIV medications that are only taken once a day. If there is resistant virus, however, these
may not work and other medication options must be used. If your disease has progressed to AIDS, your treatment may
also include drugs to combat and prevent certain infections.
Botany first year Chapter 4 sample Q&A
1. Write a brief note on cell theory. (02) marks
ANSWER
In biology, cell theory is a scientific theory which describes the properties of cells. These cells are
the basic unit of structure in all organisms and also the basic unit of reproduction. Cell theory was
eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor
Schwann. The three tenets to the cell theory are as described below:
1-All living organisms are composed of one or more cells.
2-The cell is the most basic unit of life.
3-All cells arise from pre-existing, living cells
2. Discuss the types of microscopes, and their attributes. (02) marks
ANSWER
A microscope is an instrument used to see objects that are too small for the naked eye. The most
common is the optical microscope, which uses light to image the sample. Other major types of
microscopes are the electron microscope (both the transmission electron microscope and the
scanning electron microscope) and X-ray microscope.
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of
illumination. Because the wavelength of an electron can be up to 100,000 times shorter than that
of visible light photons, the electron microscope has a higher resolving power than a light
microscope and can reveal the structure of smaller objects.
3. What is a technique to isolate cell contents? (02) marks
ANSWER
Tissue is typically homogenized in an isotonic buffer solution, as well as a pH buffer by use of a
variety of mechanisms such as grinding, mincing, chopping, pressure changes, osmotic shock,
freeze-thawing, and ultra-sound homogenization. This is done to stop osmotic damage.
Differential centrifugation is a common procedure used to separate certain organelles from whole
cells for further analysis of specific parts of cells. The homogenate is then subjected to repeated
centrifugations, each time removing the pellet and increasing the centrifugal force. Separation is
based on size and density, with larger and denser particles pellet at lower centrifugal forces. As an
example, unbroken whole cells will pellet at low speeds and short intervals such as 1,000g for 5
minutes. Smaller cell fragments and organelles remain in the supernatant and require more force
and greater times to pellet.
4. Why is the structure of plasma membrane important? (02) marks
ANSWER
The cell membrane is selectively permeable to ions and organic molecules and controls the
movement of substances in and out of cells. The basic function of the cell membrane is to protect
the cell from its surroundings. It consists of the phosphor-lipid bi-layer with embedded proteins.
Lipid bi-layers form through the process of self-assembly. The cell membrane consists primarily of
a thin layer of amphipathic phospholipids which spontaneously arrange so that the hydrophobic
"tail" regions are isolated from the surrounding polar fluid, causing the more hydrophilic "head"
regions to associate with the intracellular (cytosolic) and extracellular faces of the resulting bilayer.
5. How does fluid and mosaic model explain the structure of plasma-membrane? (02) marks
ANSWER
According to the fluid mosaic model of S. J. Singer and G. L. Nicolson (1972) biological membranes
can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse more
or less easily. Although the lipid bi-layers that form the basis of the membranes do indeed form
two-dimensional liquids by themselves, the plasma membrane also contains a large quantity of
proteins, which provide more structure. While plasma membranes are commonly described as
phosphor-lipid bi-layers, they are actually composed primarily of protein can be either peripheral
or integral to the membrane. Peripheral membrane proteins are anchored to the surface of the
membrane, while integral membrane proteins contain trans-membrane regions that pass
completely through the bi-layer.
6. Write a short note on nucleus. (02) marks
ANSWER
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells.
Eukaryotes usually have a single nucleus, but a few cell types have no nuclei, and a few others
have many. Cell nuclei contain most of the cell's genetic material, organized as multiple long linear
DNA molecules in complex with a large variety of proteins, such as histones, to form
chromosomes. The genes within these chromosomes are the cell's nuclear genome. The main
structures making up the nucleus are the nuclear envelope, a double membrane that encloses the
entire organelle and isolates its contents from the cellular cytoplasm. Because the nuclear
membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear
transport of molecules across the envelope.
7. Discuss the different modes of transportation across plasma-membrane. (02) marks
ANSWER
The cell employs a number of transport mechanisms that involve biological membranes:
Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide
(CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive
transport process. Such molecules diffuse passively through protein channels such as aquaporins
(in the case of water (H2O)).
Endocytosis is the process in which cells absorb molecules by engulfing them. The plasma
membrane creates a small deformation inward, called an invagination, in which the substance to
be transported is captured. Endocytosis is a pathway for internalizing solid particles ("cell eating"
or phagocytosis), small molecules and ions ("cell drinking" or pinocytosis), and macromolecules.
Endocytosis requires energy and is thus a form of active transport. In Exocytosis, the membrane of
a vesicle can be fused with the plasma membrane, extruding its contents to the surrounding
medium.
8. Write a short note on cell-wall. (02) marks
ANSWER
The walls of plant cells must have sufficient tensile strength to withstand internal osmotic
pressures of several times atmospheric pressure that result from the difference in solute
concentration between the cell interior and external water. Plant cell walls vary from 0.1 to
several μm in thickness. Up to three layers may be found in plant cell walls:
1-The middle lamella, a layer rich in pectins. This outermost layer forms the interface between
adjacent plant cells and glues them together.
2-The primary cell wall, generally a thin, flexible and extensible layer formed while the cell is
growing.
3-The secondary cell wall, a thick layer formed inside the primary cell wall after the cell is fully
grown. It is not found in all cell types. Some cells, such as the conducting cells in xylem, possess a
secondary wall containing lignin, which strengthens and waterproofs the wall.
9. Discuss briefly the importance of mitochondria. (02) marks
ANSWER
The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in most
eukaryotic cells. Mitochondria range from 0.5 to 1.0 μm in diameter. A considerable variation can
be seen in the structure and size of this organelle. Unless specifically stained, they are not visible.
These structures are described as "the powerhouse of the cell" because they generate most of the
cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. The organelle
is composed of compartments that carry out specialized functions. These compartments or
regions include the outer membrane, the inter-membrane space, the inner membrane, and the
cristae and matrix.
10. Write a short note on plastids. (02) marks
ANSWER
Plastids are the site of manufacture and storage of important chemical compounds used by the
cell. They often contain pigments used in photosynthesis. In plants, plastids may differentiate into
several forms, depending upon which function they play in the cell. Undifferentiated plastids
(proplastids) may develop into any of the following variants:
Chloroplasts (green plastids): for photosynthesis
Chromoplasts (coloured plastids): for pigment synthesis and storage
Leucoplasts (colour-less plastids): for starch storage
11. What is the importance of ribosomes? (02) marks
ANSWER
The ribosome is a large and complex molecular machine, found within all living cells, that serves
as the site of biological protein synthesis. A ribosome is made from complexes of RNAs and
proteins and is therefore a ribo-nucleo-protein. Each ribosome is divided into two subunits: a
smaller subunit which binds to the mRNA pattern, and a larger subunit which binds to the tRNA
and the amino acids. When a ribosome finishes reading an mRNA molecule, these two subunits
split apart. When a ribosome begins to synthesize proteins that are needed in some organelles,
the ribosome making this protein can become "membrane-bound". In eukaryotic cells this
happens in a region of the endoplasmic reticulum (ER) called the "rough ER".
ANSWER
In biology, cell theory is a scientific theory which describes the properties of cells. These cells are
the basic unit of structure in all organisms and also the basic unit of reproduction. Cell theory was
eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor
Schwann. The three tenets to the cell theory are as described below:
1-All living organisms are composed of one or more cells.
2-The cell is the most basic unit of life.
3-All cells arise from pre-existing, living cells
2. Discuss the types of microscopes, and their attributes. (02) marks
ANSWER
A microscope is an instrument used to see objects that are too small for the naked eye. The most
common is the optical microscope, which uses light to image the sample. Other major types of
microscopes are the electron microscope (both the transmission electron microscope and the
scanning electron microscope) and X-ray microscope.
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of
illumination. Because the wavelength of an electron can be up to 100,000 times shorter than that
of visible light photons, the electron microscope has a higher resolving power than a light
microscope and can reveal the structure of smaller objects.
3. What is a technique to isolate cell contents? (02) marks
ANSWER
Tissue is typically homogenized in an isotonic buffer solution, as well as a pH buffer by use of a
variety of mechanisms such as grinding, mincing, chopping, pressure changes, osmotic shock,
freeze-thawing, and ultra-sound homogenization. This is done to stop osmotic damage.
Differential centrifugation is a common procedure used to separate certain organelles from whole
cells for further analysis of specific parts of cells. The homogenate is then subjected to repeated
centrifugations, each time removing the pellet and increasing the centrifugal force. Separation is
based on size and density, with larger and denser particles pellet at lower centrifugal forces. As an
example, unbroken whole cells will pellet at low speeds and short intervals such as 1,000g for 5
minutes. Smaller cell fragments and organelles remain in the supernatant and require more force
and greater times to pellet.
4. Why is the structure of plasma membrane important? (02) marks
ANSWER
The cell membrane is selectively permeable to ions and organic molecules and controls the
movement of substances in and out of cells. The basic function of the cell membrane is to protect
the cell from its surroundings. It consists of the phosphor-lipid bi-layer with embedded proteins.
Lipid bi-layers form through the process of self-assembly. The cell membrane consists primarily of
a thin layer of amphipathic phospholipids which spontaneously arrange so that the hydrophobic
"tail" regions are isolated from the surrounding polar fluid, causing the more hydrophilic "head"
regions to associate with the intracellular (cytosolic) and extracellular faces of the resulting bilayer.
5. How does fluid and mosaic model explain the structure of plasma-membrane? (02) marks
ANSWER
According to the fluid mosaic model of S. J. Singer and G. L. Nicolson (1972) biological membranes
can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse more
or less easily. Although the lipid bi-layers that form the basis of the membranes do indeed form
two-dimensional liquids by themselves, the plasma membrane also contains a large quantity of
proteins, which provide more structure. While plasma membranes are commonly described as
phosphor-lipid bi-layers, they are actually composed primarily of protein can be either peripheral
or integral to the membrane. Peripheral membrane proteins are anchored to the surface of the
membrane, while integral membrane proteins contain trans-membrane regions that pass
completely through the bi-layer.
6. Write a short note on nucleus. (02) marks
ANSWER
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells.
Eukaryotes usually have a single nucleus, but a few cell types have no nuclei, and a few others
have many. Cell nuclei contain most of the cell's genetic material, organized as multiple long linear
DNA molecules in complex with a large variety of proteins, such as histones, to form
chromosomes. The genes within these chromosomes are the cell's nuclear genome. The main
structures making up the nucleus are the nuclear envelope, a double membrane that encloses the
entire organelle and isolates its contents from the cellular cytoplasm. Because the nuclear
membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear
transport of molecules across the envelope.
7. Discuss the different modes of transportation across plasma-membrane. (02) marks
ANSWER
The cell employs a number of transport mechanisms that involve biological membranes:
Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide
(CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive
transport process. Such molecules diffuse passively through protein channels such as aquaporins
(in the case of water (H2O)).
Endocytosis is the process in which cells absorb molecules by engulfing them. The plasma
membrane creates a small deformation inward, called an invagination, in which the substance to
be transported is captured. Endocytosis is a pathway for internalizing solid particles ("cell eating"
or phagocytosis), small molecules and ions ("cell drinking" or pinocytosis), and macromolecules.
Endocytosis requires energy and is thus a form of active transport. In Exocytosis, the membrane of
a vesicle can be fused with the plasma membrane, extruding its contents to the surrounding
medium.
8. Write a short note on cell-wall. (02) marks
ANSWER
The walls of plant cells must have sufficient tensile strength to withstand internal osmotic
pressures of several times atmospheric pressure that result from the difference in solute
concentration between the cell interior and external water. Plant cell walls vary from 0.1 to
several μm in thickness. Up to three layers may be found in plant cell walls:
1-The middle lamella, a layer rich in pectins. This outermost layer forms the interface between
adjacent plant cells and glues them together.
2-The primary cell wall, generally a thin, flexible and extensible layer formed while the cell is
growing.
3-The secondary cell wall, a thick layer formed inside the primary cell wall after the cell is fully
grown. It is not found in all cell types. Some cells, such as the conducting cells in xylem, possess a
secondary wall containing lignin, which strengthens and waterproofs the wall.
9. Discuss briefly the importance of mitochondria. (02) marks
ANSWER
The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in most
eukaryotic cells. Mitochondria range from 0.5 to 1.0 μm in diameter. A considerable variation can
be seen in the structure and size of this organelle. Unless specifically stained, they are not visible.
These structures are described as "the powerhouse of the cell" because they generate most of the
cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. The organelle
is composed of compartments that carry out specialized functions. These compartments or
regions include the outer membrane, the inter-membrane space, the inner membrane, and the
cristae and matrix.
10. Write a short note on plastids. (02) marks
ANSWER
Plastids are the site of manufacture and storage of important chemical compounds used by the
cell. They often contain pigments used in photosynthesis. In plants, plastids may differentiate into
several forms, depending upon which function they play in the cell. Undifferentiated plastids
(proplastids) may develop into any of the following variants:
Chloroplasts (green plastids): for photosynthesis
Chromoplasts (coloured plastids): for pigment synthesis and storage
Leucoplasts (colour-less plastids): for starch storage
11. What is the importance of ribosomes? (02) marks
ANSWER
The ribosome is a large and complex molecular machine, found within all living cells, that serves
as the site of biological protein synthesis. A ribosome is made from complexes of RNAs and
proteins and is therefore a ribo-nucleo-protein. Each ribosome is divided into two subunits: a
smaller subunit which binds to the mRNA pattern, and a larger subunit which binds to the tRNA
and the amino acids. When a ribosome finishes reading an mRNA molecule, these two subunits
split apart. When a ribosome begins to synthesize proteins that are needed in some organelles,
the ribosome making this protein can become "membrane-bound". In eukaryotic cells this
happens in a region of the endoplasmic reticulum (ER) called the "rough ER".
Saturday, 5 September 2015
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