NCERT Exemplar Class 9 Science Solutions Chapter 5 The Fundamental Unit of Life

Question:1

Which of the following can be made into crystal?
(a) A Bacterium
(b) An Amoeba
(c) A Virus
(d) A Sperm
Answer: (c)
Viruses are peculiar things as they are neither living nor non-living; they behave as living organism inside the body but outside the body they are non-living. Collection of virus forms a crystal which are used in scientific studies and research.

Crystal structure of hepatitis virus.
Therefore, option (c) is correct.

Question:2

A cell will swell up if
(a) The concentration of water molecules in the cell is higher than the concentration of water molecules in surrounding medium
(b) The concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell
(c) The concentration of water molecules is same in the cell and in the surrounding medium
(d) Concentration of water molecules does not matter
Answer: B
Osmosis is the movement of water from a higher concentration to lower concentration when separated by semipermeable membrane like plasma membrane.
Behavior of a cell in hypertonic solution.
Hypertonic solution is a solution whose water concentration is less compared to the solution inside the cell (cytoplasm). Due to osmosis, water moves out of the cell leading to shrinking of cell.
Behavior of cell in hypotonic solution
Hypotonic solution is a solution whose water concentration is high compared to the solution inside the cell (cytoplasm). Due to osmosis, water moves into the cell leading to bulging of cell.
Behavior of cell in Isotonic Solution
Isotonic solution is a solution whose water concentration is same compared to the solution inside the cell (cytoplasm). So, the cell stays stable (No change in shape).

Therefore, option (b) is correct.

Question:3

Chromosomes are made up of
(a) DNA
(b) protein
(c) DNA and protein
(d) RNA
Answer: (C)
DNA is packed in the form of chromosomes. The double helix structure of a DNA gets wrapped around the proteins called histones which further wrap around themselves and then they form chromosomes. So chromosomes are made up of DNA and proteins (Histones).

Therefore, option (c) is correct.

Question:4

Which of these options are not a function of Ribosomes?
(i) It helps in manufacture of protein molecules
(ii) It helps in manufacture of enzymes
(iii) It helps in manufacture of hormones
(iv) It helps in manufacture of starch molecules
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)
Answer: (c)
Ribosomes are spherical organelles which are either free in cytoplasm or attached to rough endoplasmic reticulum which play an important role in synthesis of proteins. All enzymes are proteins but not all hormones are proteins.
Statement 3 and 4 are incorrect as ribosomes are not involved in starch molecule manufacture and all hormones are not proteins.
Therefore, option (c) is correct.

Question:5

Which of these is not related to endoplasmic reticulum?
(a) It behaves as transport channel for proteins between nucleus and cytoplasm
(b) It transports materials between various regions in cytoplasm
(c) It can be the site of energy generation
(d) It can be the site for some biochemical activities of the cell
Answer: (C)
Endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets. There are two types of ER– rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture. The manufactured proteins are then sent to various places in the cell depending on need, using the ER. The SER helps in the manufacture of fat molecules, or lipids, important for cell function.
Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis. Some other proteins and lipids function as enzymes and hormones. Although the ER varies greatly in appearance in different cells, it always forms a network system. Thus, one function of the ER is to serve as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus. The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell. In the liver cells of the group of animals called vertebrates (see Chapter 7), SER plays a crucial role in detoxifying many poisons and drugs.
Therefore, option (c) is correct.

Question:6

Following are a few definitions of osmosis
Read carefully and select the correct definition
(a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane
(b) Movement of solvent molecules from its higher concentration to lower concentration
(c) Movement of solvent molecules from higher concentration to lower concentration of solution through a permeable membrane
(d) Movement of solute molecules from lower concentration to higher concentration of solution through a semipermeable membrane
Answer: (a)
Osmosis is the movement of water from a higher concentration to lower concentration when separated by semipermeable membrane like plasma membrane. First definition is the most accurate which states that:
Movement of water molecules through selective permeable membrane along concentration gradient is called osmosis.

Therefore, option (a) is correct.

Question:7

Plasmolysis in a plant cell is defined as
(a) break down (lysis ) of plasma membrane in hypotonic medium
(b) shrinkage of cytoplasm in hypertonic medium
(c) shrinkage of nucleoplasm
(d) none of them
Answer: (C)
When plant cells are placed in hypertonic solution they shrink (cytoplasm decreases) this process is known as plasmolysis.
Hypertonic solution is a solution whose water concentration is less compared to the solution inside cell (cytoplasm). Due to osmosis, water moves out of the cell leading to shrinking of cell.

Therefore, option (c) is correct.

Question:8

Which of the following are covered by a single membrane?
(a) Mitochondria
(b) Vacuole
(c) Lysosome
(d) Plastid
Answer: (c)
Lysosomes are the single membraned sac like structures present in cytoplasm which carry digestive enzymes and help in food digestion. These are known as suicide bags of cell as they dispose the digestive enzymes in extreme starvation cases and kills the cell.
Plastids are double membraned organelle
Mitochondria is double membraned organelle where pyruvate molecule is turned into ATP on the surface of the membranes.
Therefore, option (c) is correct.

Question:9

Find out the false sentences
(a) Golgi apparatus is involved with the formation of lysosomes
(b) Nucleus, mitochondria and plastid have DNA; hence they are able to make their own structural proteins
(c) Mitochondria is said to be the power house of the cell as ATP is generated in them.
(d) Cytoplasm is called as protoplasm
Answer : (d)
Protoplasm includes both cytoplasm and nucleus combined together. On the other hand, cytoplasm means the cellular fluid inside the cell membrane apart from the organelles.
Mitochondria is double membraned organelle where pyruvate molecule is turned into ATP on the surface of the membranes. ATP is the energy currency of a cell and this is produced only by mitochondria. This is the reason it is known as power house of cell.
DNA and Ribosomes are the main requirement if and organisms wants to self-replace and both these are found in Mitochondria plastid and nucleus therefore they are capable of making their own structures.
One of the functions of Golgi apparatus is to make lysosomes apart from plasma membrane synthesis and waste disposal.
Therefore, option (d) is correct.

Question:10

Find out the correct sentence
(a) Enzymes packed in Lysosomes are made through RER (rough endoplasmic reticulum)
(b) Rough endoplasmic reticulum and smooth endoplasmic reticulum produce lipid and protein respectively
(c) Endoplasmic reticulum is related with the destruction of plasma membrane
(d) Nucleoid is present inside the nucleoplasm of eukaryotic nucleus
Answer : (a)
Enzymes are made by rough endoplasmic reticulum as they have ribosomes which synthesize proteins. All enzymes are proteins by nature.
Rough Endoplasmic reticulum and smooth endoplasmic reticulum make proteins and lipids respectively; not the other way around, like given it the question.
Nucleoid and nucleoplasm are present inside the nuclear membrane of eukaryotic nucleus.
Endoplasmic reticulum is not related with the destruction of plasma membrane. Lysosomes are related with plasma membrane and overall cell destruction due to the presence of powerful digestive enzymes.
Therefore, option (a) is correct.

Question:11

Which cell organelle plays a crucial role in detoxifying many poisons and drugs in a cell?
(a) Golgi apparatus
(b) Lysosomes
(c) Smooth endoplasmic reticulum
(d) Vacuoles
Answer: (c)
Smooth endoplasmic reticulum is responsible for the detoxification of a cell. In human, liver cells are equipped with a lot of smooth endoplasmic reticulum which detoxes drugs, alcohol and poison.
Therefore, option (c) is correct.

Question:12

The proteins and lipids, essential for building the cell membrane, are manufactured by
(a) rough endoplasmic reticulum
(b) golgi apparatus
(c) plasma membrane
(d) mitochondria
Answer : (a)
The smooth endoplasmic reticulum helps in the manufacture of fat molecules, or lipids, important for cell function.
The rough endoplasmic reticulum helps in the manufacture of proteins.
Therefore, option (a) is correct.

Question:13

The undefined nuclear region of prokaryotes are also known as
(a) nucleus
(b) nucleolus
(c) nucleic acid
(d) nucleoid
Answer : (d)
In prokaryotic cells, there is no well that defines nucleus or nuclear membrane to bind the nuclear material. Genetic material is Circular DNA in prokaryotes which lies naked in cytoplasm and this region is called as nucleoid.
Therefore, option (d) is correct.

Question:14

The cell organelle involved in forming complex sugars from simple sugars are
(a) endoplasmic reticulum
(b) ribosomes
(c) plastids
(d) golgi apparatus
Answer : (d)
Golgi apparatus is the organelle which is responsible for packaging and storing proteins manufactured by ribosomes. This organelle makes complex sugars from simple sugars needed for cell membrane. Also it packs digestive enzymes in a circular membrane known as lysosomes.
Therefore, option (d) is correct.

Question:15

Which out of the following is not a function of vacuole?
(a) Storage
(b) Providing turgidity and rigidity to the cell
(c) Waste excretion
(d) Locomotion
Answer: (d)
Vacuoles are storage sacs for solid or liquid contents. In plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to the cell. Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids, sugars, various organic acids and some proteins. In some unicellular organisms, specialized vacuoles also play important roles in expelling excess water and some wastes from the cell. But vacuoles are not involved in locomotion of cells.
Therefore, option (d) is correct.

Question:16

Amoeba acquires its food through a process, termed
(a) exocytosis
(b) endocytosis
(c) plasmolysis
(d) exocytosis and endocytosis both
Answer : (b)
Amoeba obtains its food through the process of phagocytosis. It is a common way of feeding in protozoans. The amoeba’s plasma membrane forms a pocket around the food material and engulfs the solid material, forming a food vacuole in cytoplasm. The contents are digested by lysosomes which contain digestive enzymes.
Exocytosis is a form of active transport and bulk transport in which a cell transports molecule out of the cell by secreting them through an energy-dependent process.
Endocytosis is a cellular process in which substances are brought into the cell.
Therefore, option (b) is correct.

Question:17

Cell wall of which one of these is not made up of cellulose?
(a) Bacteria
(b) Hydrilla
(c) Mango tree
(d) Cactus
Answer : (a)
Cellulose is a polysaccharide (long chain of sugars or complex sugar) which is found in the cell wall of plants which gives rigidity and protects the cell. So, in the above options; hydrilla, mango tree, cactus belong to plant but bacteria does not. Bacteria cell wall is made up of peptidoglycan which is also a polysaccharide.
Therefore, option (a) is correct.

Question:18

Silver nitrate solution is used to study
(a) endoplasmic reticulum
(b) golgi apparatus
(c) nucleus
(d) mitochondria
Answer: (b)
Golgi apparatus was discovered by Camillo Golgi using black reaction. Here, the cells are stained in a weak silver nitrate solution which is particularly valuable in tracing the processes and most delicate ramifications of cells.
Therefore, option (b) is correct.

Question:19

Organelle other than nucleus, containing DNA is
(a) endoplasmic reticulum
(b) golgi apparatus
(c) mitochondria
(d) lysosome
Answer : (c)
Mitochondria, plastids are the only organelles which have their own genetic material (DNA) apart from nucleus. These organelles replicate on their own without the involvement of the cell.
Therefore, option (c) is correct.

Question:20

Kitchen of the cell is
(a) mitochondria
(b) endoplasmic reticulum
(c) chloroplast
(d) golgi apparatus
Answer : (c)
Chloroplast is the organelle which makes the food for the plant cells by taking raw material like water, minerals, carbon dioxide and sunlight and converts to glucose.
This is the reason chloroplast are known as the kitchen of the cell.
Therefore, option (c) is correct.

Question:21

Lipid molecules in the cell are sythesized by
(a) smooth endoplasmic reticulum
(b) rough endoplasmic reticulum
(c) golgi apparatus
(d) plastids
Answer : (a)
The Smooth endoplasmic reticulum helps in the manufacture of fat molecules, or lipids, important for cell function.
The smooth endoplasmic reticulum (SER) has functions such as it synthesizes lipids, phospholipids and steroids. Cells which secrete these products, such as those in the testes, ovaries and sebaceous glands have an abundance of smooth endoplasmic reticulum.
Therefore, option (a) is correct.

Question:22

Cell arises from pre-existing cell was stated by
(a) Haeckel
(b) Virchow
(c) Hooke
(d) Schleiden
Answer : (b)
In 1938, Schleiden proposed the idea that plants are made of cells.
In 1939, Schwann independently proposed the idea that plants and animals are made of cells. Also known as cell theory later.
In 1855, R. Virchow refined the cell theory by stating that cells arise from pre-existing cell.
Therefore, option (b) is correct.

Question:23

Cell theory was given by
(a) Schleiden and Schwann
(b) Virchow
(c) Hooke
(d) Haeckel
Answer: (c)
In 1938, Schleiden proposed the idea that plants are made of cells.
In 1939, Schwann independently proposed the idea that plants and animals are made of cells. Also known as cell theory later.
In 1855, R. Virchow refined the cell theory by stating that cells arise from pre-existing cell.
Postulates of cell theory
1. All organisms are made of cells and cell products
2. Every organism starts as a single cell organism.
3. All cell arises from preexisting cells.
Therefore, option (c) is correct.

Question:24

The only cell organelle seen in prokaryotic cell is
(a) mitochondria
(b) ribosomes
(c) plastids
(d) lysosomes
Answer (b)
Prokaryotic organisms lack membrane bound organelles like plastids, lysosomes, mitochondria etc.
All the cells need to have ribosomes to manufacture proteins and prokaryotes are equipped with 70S ribosomes.
Therefore, option (b) is correct.

Question:25

Organelle without a cell membrane is
(a) ribosome
(b) golgi apparatus
(c) chloroplast
(d) nucleus
Answer : (a)
Ribosomes are the only organelles where cell membrane is missing. It helps in the manufacturing of proteins. All the other organelles are membrane bound in nature.
Therefore, option (a) is correct.

Question:26

is
(a)
(b)
(c)
(d)
Answer : (a)
Micro meter also known as micron is a unit used to measure small things in nature.

Micrometer is represented with symbol
Therefore, option (a) is correct.

Question:27

Lysosome arises from
(a) endoplasmic reticulum
(b) golgi apparatus
(c) nucleus
(d) mitochondria
Answer : (b)
Golgi apparatus is the organelle which is responsible for packaging and storing proteins manufactured by ribosomes. This organelle makes complex sugars from simple sugars needed for cell membrane. It also packs digestive enzymes in a circular membrane known as lysosomes.
Therefore, option (b) is correct.

Question:28

Living cells were discovered by
(a) Robert Hooke
(b) Purkinje
(c) Leeuwenhoek
(d) Robert Brown
Answer : (c)
Cells were first discovered by Robert Hooke in 1665. He observed the cells in a cork slice with the help of a primitive microscope. Leeuwenhoek (1674), with the improved microscope, discovered the free-living cells in pond water for the first time. So, Robert Hooke discovered dead cell but Leeuwenhoek was responsible for the discovery of living cells.
Therefore, option (c) is correct.

Question:29

Select the odd one out
(a) The movement of water across a semi permeable membrane is affected by the amount of substances dissolved in it.
(b) Membranes are made of organic molecules like proteins and lipids
(c) Molecules soluble in organic solvents can easily pass through the membrane.
(d) Plasma membranes contain chitin sugar in plants
Answer : (d)
(a) The movement of water across a semi permeable membrane is affected by the amount of substances dissolved in it. Water moves from higher concentration to lower concentration.
(b) Membranes are made of organic molecules like proteins and lipids.
(c) Membrane is lipophilic, so molecules soluble in organic solvents can easily pass through the membrane.
The hydrophobic molecules (which are soluble in organic solvents) can pass easily through the membrane but water needs channels to move through the membrane as they are polar in nature.
(d) All the cellular constituents are bound by plasma membrane.
Plasma membrane is a semipermeable membrane which is composed of two layers of lipids. Plasma membrane does not contain any kind of sugar.
Cell walls of fungi contain chitin sugar.
Therefore, option (d) is correct answer.

Question:30

Why are lysosomes known as ‘suicide-bags’ of a cell?
Answer :
Lysosomes are rich in hydrolytic enzymes like (lipase, Proteases, Carbohydras, nucleases) capable of digesting organic molecule.
How different organic molecules are broken in lysosomes:
Fats ---- (lipases) ---- Glycerides
Protein ---- (Proteases) ---- Peptones + Peptides
Carbohydrates ---- (Carbohydras) ---- Disaccharides + Monosaccharides
DNA/RNA ---- (Nucleases) ---- Nucleotides
Lysosomes help in digestion but in extreme starvation situation lysosomes release hydrolytic enzymes into cell digesting the cell constituents, and eventually killing the cell. That is the reason they are called as suicidal bags.

Question:31

Do you agree that “A cell is a building unit of an organism”? If yes, explain why?
Answer:
Yes, cell is the building unit of life on organism. All living cells are composed of cells. Cells have many cell organelles, all together performing different functions. In multicellular organisms, group of cells act as an organism but cell is the basic unit. In unicellular organisms, single cell itself acts as an organism but nothing less than a cell can exist as living organism individually.

Question:32

Why does the skin of your finger shrink when you wash clothes for a long time?
Answer:
Skin cells lack cell wall and their cell membrane is directly exposed to soap solution or detergent water which acts as hypertonic solution compared to a cellular fluid. When cells are exposed to hypertonic solution, water moves out of the cell as cell membrane is semi permeable and this leads to shrinking of skin cells which makes your fingers look shrinked. The process of water moving out of a cell in a hypertonic solution is called exosmosis.

Question:33

Why is endocytosis found in animals only?
Answer:
Endocytosis is a process through which cell absorbs surrounding food/nutrients by engulfing through a semi permeable membrane.
It is possible only in animal cell as they lack cell wall which restricts fluid movement necessary for engulfing.

Question:34

A person takes concentrated solution of salt, after sometime, he starts vomiting. What is the phenomenon responsible for such situation? Explain.
Answer:
Concentrated salt solution is hypertonic compared to cellular fluids in human cells which leads to exosmosis (movement of water from cells).
Movement of water from cells leads to irritation and death of cells/ in our body which sets a reflex action leading to forceful expulsion of salt solution as vomit.

Question:35

Name any cell organelle which is non membranous.
Answer:
Non-membranous organelles are not surrounded by a membrane.
Ribosomes are the non-membrane organelles which are on rough endoplasmic reticulum. The main function of ribosomes is to synthesis proteins.

Question:36

We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, amino acids, fatty acids, glycerol etc.
What mechanisms are involved in absorption of digested food and water?
Answer:
Various methods of absorption of food:
1. Diffusion: It is a physical process which does not need a membrane. The movement of substance is from higher concentration to lower concentration.
For example, this the process which food is distributed equally throughout the cell.
2. Facilitated: These require carrier proteins for the transportation of substances which does not works against the concentration gradient.
For example, Fructose absorption through cell membrane.
3. Active transport: This process requires carrier proteins and ATP energy for the movement against concentration gradient.
For example, movement of glucose and amino acids through membrane.
4: Osmosis: Movement of solvent from higher concentration to lower concentration.
For example, Water is absorbed through this process.

Question:37

If you are provided with some vegetables to cook. You generally add salt into the vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?
Answer:
The mechanism responsible for this is exosmosis.
The salt solution acts as a hypertonic solution compared to cellular environment which leads to movement of water from inside of cell to outside to restore the osmotic balance.

Question:38

If cells of onion peel and RBC are separately kept in hypotonic solution, what among the following will take place? Explain the reason for your answer.
(a) Both the cells will swell.
(b) RBC will burst easily while cells of onion peel will resist the bursting to some extent.
(c) a and b both are correct.
(d) RBC and onion peel cells will behave similarly.
Answer:
Option C is correct. When onion cell and red blood cells are placed in hypotonic solution, it will led to endosmosis (movement of water into cell) leading to the swelling of cell.
In the case of red blood cells, they burst easily compared to that of onion cell as red blood cells lack cell membrane which protects the cell from bursting.

Question:39

Bacteria do not have chloroplast but some bacteria are photoautorophic in nature and perform photosynthesis. Which part of bacterial cell performs this?
Answer:
Bacterial cell does not have chloroplast but yet some photoautotrophic bacteria perform photosynthesis due to presence of chlorophyll in membranes of plasma membrane which absorbs light energy. These reaction center exists in the form of sacs tubes or sheets depending on the amount of surface area needed.

Question:40

Match the following A and B
(A) (B)
(a) Smooth endoplasmic reticulum (i) Amoeba
(b) Lysosome (ii) Nucleus
(c) Nucleoid (iii) Bacteria
(d) Food vacuoles (iv) Detoxification
(e) Chromatin material and nucleolus (v) Suicidal bag
Answer:
(a) Smooth endoplasmic reticulum (iv) Detoxification
Smooth endoplasmic reticulum is responsible for the excretion process of a cell.
(b) Lysosome (v) Suicidal bag
Lysosomes help in digestion, but in extreme starvation situation lysosomes release hydrolytic enzymes into cell digesting the cell constituents. Eventually, this kills the cell. That is the reason they are called as suicidal bags.
(c) Nucleoid (iii) Bacteria
Genetic material is circular DNA in prokaryotes which lies naked in cytoplasm and this region is called as nucleoid.
(d) Food vacuoles (i) Amoeba
Amoeba consumes food by making food vacuoles.
(e) Chromatin material and nucleolus (ii) Nucleus
Chromatin and nucleolus are present inside the nucleus.

Question:41

Write the name of different plant parts in which chromoplast, chloroplast and leucoplast are present.
Answer:
Chromoplast are present in flowers (petals which are colorful), fruits (fruits are colorful like tomatoes etc.) as these contain colored pigments.
Chloroplast are found in leaves and young stems and actively take part in photosynthesis. Leucoplasts are found everywhere. These are colorless and primarily store food. These plastids are interchangeable from one to another at the time of necessity.

Question:42

Name the organelles which show the analogy written as under
(a) Transporting channels of the cell——
(b) Power house of the cell——
(c) Packaging and dispatching unit of the cell——
(d) Digestive bag of the cell——
(e) Storage sacs of the cell——
(f) Kitchen of the cell——
(g) Control room of the cell——
Answer:
a) Endoplasmic reticulum: transporting channels of the cell as it is connected to nuclear membrane.
b) Mitochondria is the power house of the cell as it converts pyruvate molecules to ATP which is the energy currency of a cell.
c) Golgi complex is responsible for the packaging and dispatching unit of cell.
d) Lysosomes are the digestive bag of a cell as it contains digestive enzymes.
e) Vacuoles are the storage sacs of the cell as they store food and other cellular materials.
f) Chloroplast is the organelle which makes the food for the plant cells by taking raw material like water, minerals, carbon dioxide and sunlight and converts to glucose. This is the reason chloroplast are known as the kitchen of the cell.
g) Nucleus is the control room of the cell as it regulates all the cellular activity due to the presence of genetic material.

Question:43

How is a bacterial cell different from an onion peel cell?
Answer:
Bacterial cell: Prokaryote.
Onion Peel: Eukaryote.

Question:44

How do substances like carbon dioxide and water move in and out of the cell?
Answer:
The movement of gas across membrane takes place by diffusion. It does not require any energy as motion of molecules takes place from region of its higher concentration to lower concentration.
Movement of water is by osmosis which is driven by water potential gradient across a membrane.

Question:45

How does amoeba obtain its food?
Answer:
Amoeba obtains its food the process of phagocytosis. It is a common way of feeding in protozoans. The amoeba’s plasma membrane forms a pocket around the food material and engulfs the solid material, forming a food vacuole in cytoplasm. The contents are digested by lysosomes which contain digestive enzymes.

Question:46

Name the two organelles in a plant cell that contain their own genetic material and ribosomes.
Answer:

The two organelles in a plant cell that contain their own genetic material and ribosomes are plastids and mitochondria. Hence they are also known as semi-autonomous cell organelles.

Question:47

Why are lysosomes also known as “scavengers of the cells”?
Answer:
Lysosomes contain hydrolytic enzymes. These enzymes hydrolyze worn out and improperly working cell organelles and also digest cellular debris.
Therefore lysosomes are referred as scavengers of the cells.

Question:48

Which cell organelle controls most of the activities of the cell?
Answer:
Nucleus is the cell organelle which controls most of cellular activities. Nucleus is a double membrane bound structure containing genetic material and nucleolus. Nucleolus is site for synthesis of ribosomes. Nuclear membrane extensions give rise to endoplasmic reticulum, genetic material important for hereditary transmission and protein synthesis.

Question:49

Which kind of plastid is more common in
(a) roots of the plant
(b) leaves of the plant
(c) flowers and fruits
Answer:
a) Roots of the plants – leucoplast for storage of food material. Roots do not perform photosynthesis and are colorless (leucoplast are colorless).
b) Leaves of plants – the major place where photosynthesis takes place. They have chloroplasts and are green in color.
c) Flowers and fruits – contain chromoplasts which give color to petals of flower and fruits.

Question:50

Why do plant cells possess large sized vacuole?
Answer:
Vacuoles are storage sacs for solid or liquid contents. In plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to the cell. Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids, sugars, various organic acids and some proteins. In some unicellular organisms, specialized vacuoles also play important roles in expelling excess water and some wastes from the cell. But vacuoles are not involved in locomotion of cells.

Question:51

How are chromatin, chromatid and chromosomes related to each other?
Answer:
Inside the nucleoplasm, a tangled mass of thread-like structures is called chromatin. These are purely composed of DNA and histone proteins are used to pack it.
When a cell starts to divide, the tangled mass of chromatin condenses into rod-like bodies called chromosomes. The chromosomes contain stretches of DNA which carry information for protein synthesis.
A chromatid is one copy of duplicated chromosome which is generally joined to the other copy by a centromere.

Question:52

What are the consequences of the following conditions?
(a) A cell containing higher water concentration than the surrounding medium
(b) A cell having low water concentration than the surrounding medium.
(c) A cell having equal water concentration to its surrounding medium.
Answer:
a) Cells contain higher water content than surrounding leading to exosmosis (loss of water from cell in the presence of hypertonic environment).
b) Cells having low water concentration than the surrounding medium leads to endosmosis (movement of water into the cell in the presence of hypotonic solution).
c) Cells having equal water concentration to its surrounding medium: have no net water movement across the membrane. Therefore, isotonic.

Question:53

Draw a plant cell and label the parts which
(a) determines the function and development of the cell
(b) packages materials coming from the endoplasmic reticulum
(c) provides resistance to microbes to withstand hypotonic external media without bursting
(d) is site for many biochemical reactions necessary to sustain life.
(e) is a fluid contained inside the nucleus
Answer:

a) Nucleus determines the function and development of cell
b) Golgi apparatus packages materials coming from the endoplasmic reticulum
c) Cell wall provides resistance to microbes to withstand hypotonic external media without bursting
d) Nucleolus is site for many biochemical reactions necessary to sustain life.
e) Nucleoplasm is a fluid contained inside the nucleus

Question:54

Illustrate only a plant cell as seen under electron microscope. How is it different from animal cell?
Answer:

Difference between Plant cell and animal cell
1. Chloroplast are present in plant cell as they make their own food but these are completely absent in animal cells.
2. Plant cells have cell wall predominately made of cellulose, on the other hand animals lack cell wall completely.
3. A very large vacuole is found in plant cells which manages the cell pressure but not in an animal cell.

Question:55

Draw a neat labelled diagram of an animal cell.
Answer:

Question:56

Draw a well labelled diagram of a eukaryotic nucleus. How is it different from nucleoid?
Answer:

Major difference between eukaryotic and prokaryotic nucleus:
1. Eukaryotic nucleus is membrane bound but prokaryotic nucleus is membrane less.
2. Prokaryotic cells does not contain DNA in the form of chromosomes.
3. Prokaryotic cells does not possess nucleolus as there is no membrane separated nucleolus and cytoplasm.

Question:57

Differentiate between rough and smooth endoplasmic reticulum. How is endoplasmic reticulum important for membrane biogenesis?
Answer:
Differences between Rough Endoplasmic Reticulum & Smooth Endoplasmic Reticulum.

Role of smooth endoplasmic reticulum and rough endoplasmic reticulum: In cell membrane, mainly made up of lipids (40-45%) and proteins (50-60%), endoplasmic reticulum with ribosomes is actively involved in synthesis of proteins and enzymes. Smooth endoplasmic reticulum is involved in the synthesis of lipids which are the key constituents of cell membrane. This is how rough endoplasmic reticulum and smooth endoplasmic reticulum helps in building cell membrane.

Question:58

In brief state what happens when
(a) dry apricots are left for some time in pure water and later transferred to sugar solution?
(b) a Red Blood Cell is kept in concentrated saline solution?
(c) the Plasma-membrane of a cell breaks down?
(d) rheo leaves are boiled in water first and then a drop of sugar syrup is put on it?
(e) golgi apparatus is removed from the cell?
Answer :
a) Dry apricot placed in water for some time swells due to endoosmosis and later transferred to sugar solution shrinks due to exosmosis (sugar solution acts as hypertonic to swelled apricot in water).
b) A red blood cell kept in concentrated saline solution loses water and shrinks because of exosmosis as the saline solution is hypertonic to Red blood cells cellular fluid. This leads to outward movement of water from cell.
c) When the plasma membrane of a cell breaks down, all the cellular contents such as cytoplasm, cell organelles etc. scatters/spill out. Plasma membrane acts as boundary and packing structure which keeps its contents intact and differentiated from surroundings.
d) When rheo leaf is boiled first and then a drop of sugar syrup is put on it, osmosis does not take place due to death of plasma membrane.
e) Golgi complex: key function is modifying, packing and transferring the proteins syntheses by ribosomes. Thus when Golgi complex is removed, the cell function is hampered.

Question:59

Draw a neat diagram of plant cell and label any three parts which differentiate it from animal cell.
Answer:
Cell wall, Vacuole and Chloroplast these are the three organelles which are fond only in plants but not in animal cell.