Download The Fundamental Unit of Life Introduction The cells that make up our

The Fundamental Unit of Life
Introduction
The cells that make up our body are so small that you could fit over 200 of them on the full stop at the
end of this sentence.
Cell - A Unit of Life
All living organisms, whether plants or animals, are made up of microscopic units called cells. The cell
occupies the same central position in biology as the atom in the physical sciences.
Structure of Cell
Cells vary in shape and size. They may be oval, spherical, rectangular, polygonal, spindle shaped, star
shaped, rod-shaped or totally irregular like the nerve cell.
Cell Organelles
Some of the cell organelles are Endoplasmic Reticulum (ER), Golgi Apparatus, Lysosomes,
Peroxisomes, Ribosomes, Centrosome, Mitochondria, Plastids.
Activities using the Microscope
You need to get acquainted with the usage of the microscope, for observing cells.;
Prokaryotic and Eukaryotic Cells
The structure of the cell that we have studied so far is that of a eukaryotic cell.
Types of Cell Division
Cell division is a method by which new cells are originated from pre-existing cells. The formation of
daughter amoebae in amoeba, the development of sex cells and the growth of a young animal or plant into
an adult, all involve cell multiplication.
Mitosis
Mitosis is a type of cell division that occurs in the somatic (body) cells. A diploid (2n) parent cell gives
rise to two diploid (2n) daughter cells.
Meiosis
Meiosis is a cell division occurs in reproductive cells (gametes). The male gamete is known as the
sperm in animals and the female gamete is known as the ovum (egg).
Mitosis and Meiosis - A Comparison
Man has 46 chromosomes, and these occur in pairs i.e., diploid condition.
Question (1): Why were the scientists not able to observe most of the cell organelles before 1940?
Answer: Before 1940, scientists could view the cell only under a light microscope. The invention of the electron
microscope in 1940 enabled the scientists to observe the cell in greater detail.
Question (2): What is the function of the cell wall?
Answer: The cell wall lies outside the plasma membrane and is responsible for providing
structural strengths to the plants.
Question (3): Why are lysosomes called digestive bags or suicide bags?
Answer:
They serve as intracellular digestive system
They destroy any foreign material inside the cell
They also remove the worn out and poorly working cell organelles by digesting them to make
way for a replacement
They may even digest away the entire damaged or dead cell containing them
Question (4): Why are peroxisomes mostly found in kidney and liver cells?
Answer: Peroxisomes contain powerful oxidative enzymes, which specialize in carrying out
certain oxidative reactions, in order to remove toxic substances.
Question (5): Why are mitochondria also called 'The Power House of cell'?
Answer: Energy in the food molecules is converted here (in the mitochondria) into usable
energy and stored as ATP molecules. Hence, they are called the power house of the cells.
Question (6): There would be no plant life if chloroplasts did not exist. Justify.
Answer: Chloroplasts contain the pigment chlorophyll which is responsible for food preparation
by photosynthesis. Hence, if there were no chloroplasts then there would not have been plant
life.
Question (7): Why is the golgi apparatus called the secretory organelle of the cell?
Answer: This is because it packages material synthesized in the ER and dispatches it to
intracellular and (plasma membrane and lysosomes) extracellular targets.
Question (8): Why is variation not possible in mitotic division of cells?
Answer: In mitosis, the cell divides into two (each having the same number of cells as the
mother cell) giving rise to two identical daughter cells. Hence, variation is not possible.
Question (9): The daughter cell of meiotic division is different from the parent cells. Explain.
Answer: In meiosis, exchange of genes takes place between the two germ cells and hence, the
daughter cell will differ from the parent cells.
Question (10): Differentiate between smooth and rough endoplasmic reticulum.
Differences Between Smooth and Rough Endoplasmic
Reticulum
Answer:
Question (11): Give the importance of cristae in mitochondria.
Answer: The finger-like cristae present in the inner-folded membrane greatly increase the
surface area of the membrane.
Question (12): Give one similarity and one dissimilarity between plastids and mitochondria.
Answer:
Similarity: Their structures are more or less the same.
Dissimilarity: Mitochondria have cristae which are absent in plastids.
Question (13): In many plant cells the nucleus and other cell organelles are pushed near the
boundary walls. Explain.
Answer: In plant cells, a single prominent vacuole occupies 90% of the volume of a cell and
hence, all the organelles are pushed to the side of the cell.
Question (14): Differentiate between the cell of an elephant and a plant cell (2 differences).
Answer:
Differences Between the Cell of an Elephant and a Plant Cell
Question (15): During cell division, the number of chromosomes in a cell becomes half of what
it was initially. What type of cell is it? Name the type of cell divison.
Answer: It is a germ cell.
The type of cell division is meiosis.
Question (16): Why does not a child exactly resemble his father or mother?
Answer: A child does not exactly resemble his father or mother because the sperm and egg
cells undergo meiotic division which leads to variation.
Question (17): Identify the diagrams given below. To which stage of mitosis do they belong?
Given reasons.
Answer: a) Metaphase, because the chromosomes have arranged themselves in the equatorial
plate.
b) Anaphase, because the sets of daughter chromosomes are being pulled to the opposite
poles.
Question (18): In which phase of cell division do the following occur:
a) Disappearance of nuclear envelope
b) Development of spindle
c) Reappearance of nuclear membrane
d) Reorganization of nucleus at the poles of the dividing cells
Answer: a) Disappearance of nuclear envelope: Prophase
b) Development of spindle: Metaphase
c) Reappearance of nuclear membrane: Telophase
d) Reorganization of nucleus at the poles of the dividing cells: Anaphase
Question (19): Give two characteristics unique to meiotic divison.
Answer: Two characteristics unique to meiotic divison are:
It takes place only in germ cells
Crossing over takes place
Question (20): Identify the odd one out: nucleus, plastid, mitochondria, peroxisomes.
Answer: Plastid is the odd one out. It is the only organelle out of the above not present in
animal cells.
Question (21): What is a cell?
Answer: A cell is the structural and functional unit of living organisms.
Question (22): What are the chief components of the nucleus?
Answer: The chief components of the nucleus are:
Chromatin
Nucleolus
Question (23): Name two components that the cell membrane encloses.
Answer: The two components that the cell membrane encloses are:
Nucleus
Cytoplasm
Question (24): What are the two types of endoplasmic reticulum (ER)?
Answer: The two types of endoplasmic reticulum are:
Rough ER
Smooth ER
Question (25): Which organelle is most vital for the survival of a cell?
Answer: Nucleus is most vital for the survival of a cell.
Question (26): Define the endoplasmic reticulum.
Answer: It is a membrane network enclosing a fluid filled lumen which almost fills up the
intracellular cavity.
Question (27): Define golgi apparatus.
Answer: Golgi apparatus consists of a set of membrane bound, fluid filled vesicles, vacuoles
and flattened closed sacs called cisternae which are placed one on top of the other in parallel
rows.
Question (28): Who discovered cells?
Answer: Robert Hooke discovered cells.
Question (29): What is the cell theory? Who proposed it? When?
Answer: All plants and animals are composed of cells and that the cell is the basic unit of life.
Cell theory was proposed by M.Schleiden in 1838 and T.Schwan in 1839.
Question (30): What are lysosomes?
Answer: Lysosomes are simple, tiny spherical sac-like structures evenly distributed in the
cytoplasm.
Question (31): What are peroxisomes?
Answer: They are small spherical organelles containing powerful oxidative enzymes. They are
bound by a single membrane and are mostly found in kidney and liver cells.
Question (32): Name the important function of peroxisomes.
Answer: Important function of peroxisomes is detoxification or removal of toxic substances.
Question (33): What is the difference between vacuoles of plant and animal cells?
Answer: In plant cells they are large and permanent and in animal cells they are small and
temporary.
Question (34): Which cell organelle is responsible for release of energy as ATP?
Answer: Mitochondria is responsible for release of energy as ATP.
Question (35): Name the four phases of mitosis.
Answer: The four phases of mitosis are:
Prophase
Metaphase
Anaphase
Telophase
Question (36): How many daughter cells are produced in the case of meiosis?
Answer: Four daughter cells are produced in the case of meiosis.
Question (37): When and how is the cell plate formed?
Answer: A cell plate is formed during telophase of mitosis when two cells are separated.
Question (38): In meiosis, why is a reduction in number of chromosomes necessary in the germ
cell?
Answer: If the gametes are diploid (2n), then on fertilization the zygote will contain twice the
number of diploid chromosomes (4n). To avoid this, germ cells undergo reduction division.
Question (39): Give two properties that are unique to meiosis.
Answer: The two properties that are uniques to meiosis are:
Chromosome number in gametes becomes half
Exchange of genes results in variation
Question (40): Give two differences between Meiosis and Mitosis.
Answer:
The Fundamental Unit of Life
Question (1): The approximate number of cells in a normal human body is ____.
1. 10
2. 100
3. 1014
4. 10144
Ans: 3
Question (2): Tick the wrong choice: Plasma or cell membrane is ____.
1. outer covering of each cell
2. made of lipids and proteins
3. superheated gases
4. a mechanical barrier for the protection of inner cell contents
Ans: 3
Question (3): Mitochondria are also called _____.
1. suicide bags
2. digestive bags
3. protein synthesizers
4. power house of the cell
Ans: 4
Question (4): ATP stands for _____.
1. Adenosine triphosphate
2. Adenosine diphosphate
3. Advanced tactical plane
4. Adenosine terphosphorus
Ans: 1
Question (5): The correct order of the phases in mitosis are ____.
1. prophase, telophase, metaphase, anaphase
2. prophase, metaphase, anaphase, telophase
3. telophase, anaphase, metaphase, prophase
4. metaphase, telophase, anaphase, prophase
Ans: 2
Question (6): The resting or non-dividing stage between two successive mitotic divisions is called ____.
1. metaphase
2. telophase
3. interphase
4. prophase
Ans: 3
Question (7): Centrosomes are present in _____.
1. animal cells only
2. plant cells only
3. in both plant cells and animal cells
4. in neither plant cells nor animal cells
Ans: 1
Question (8): Vacuoles (in plant cells) _____.
1. produce energy for the cell
2. synthesize proteins
3. defend the cell
4. provide turgidity and rigidity to plant cells
Ans: 4
Question (9): Organelle not present in animal cells is _____.
1. plastid
2. centrosome
3. nucleus
4. mitochondria
Ans: 1
Question (10): The “secretory organelle― of the cell is also called ____.
1. ribosome
2. golgi apparatus
3. peroxisomes
4. centrosomes
Ans: 2
Question (11): The power house of a cell is ____.
1. chloroplast
2. mitochondrion
3. nucleolus
4. vacuole
Ans: 2
Question (12): The 'Scavengers' or 'Digestive bags' of a cell are ____.
1. chromosomes
2. centrosomes
3. lysosomes
4. ribosomes
Ans: 3
Question (13): The site of oxidation in a cell is the _____.
1. mitochondrion
2. endoplasmic reticulum
3. golgi apparatus
4. ribosome
Ans: 1
Question (14): Lysosomes are reservoirs of ____.
1. fat
2. secretory glycoproteins
3. RNA
4. hydrolytic enzymes
Ans: 4
Question (15): The network of endoplasmic reticulum is present in the ____.
1. nucleus
2. chromosome
3. cytoplasm
4. golgi apparatus
Ans: 3
Question (16): Centrioles are associated with ____________.
1. digestion
2. respiration
3. reproduction
4. cell division
Ans: 4
Question (17): A cell has 4 chromosomes. After mitotic cell division the number of chromosomes in the
daughter cell would be __________.
1. 8
2. 4
3. 16
4. 32
Ans: 2
Question (18): Synapsis occurs during __________.
1. Mitosis
2. Meiosis
3. Amitosis
4. None of the above
Ans: 2
Question (19): Division of cytoplasm is known as ______________.
1. Karyokinesis
2. Plasmolysis
3. Cytokinesis
4. None of the above
Ans: 3
Question (20): The point where crossing over of chromatids takes place is ___.
1. chiasma
2. kinetochore
3. centromere
4. chromomere
Ans: 1
Question (21): The largest animal cell is ____.
1. ostrich egg
2. amoeba
3. red blood corpuscle
4. human sperm
Ans: 1
Question (22): The organism that is an exception to the cell theory is ____.
1. virus
2. bacteria
3. amoeba
4. paramecium
Ans: 1
Question (23): The largest cell in the human body is ___________.
1. nerve cell
2. muscle cell
3. liver cell
4. kidney cell
Ans: 1
Question (24): Double membrane is absent in ______________.
1. lysosomes
2. chloroplast
3. nucleus
4. mitochondria
Ans: 4
Question (25): Organisms lacking nucleus and membrane bound organelle are _________.
1. diploids
2. prokaryotes
3. haploids
4. eukaryotes
Ans: 2