🟦 QUESTION 1
Differentiate between the following pairs of terms based on the clues given in parentheses:
(i) Cell membrane and cell wall — permeability
(ii) RER and SER — structure
(iii) Chloroplasts and chromoplasts — pigments
🟩 ANSWER
(i) Cell membrane and cell wall
| Cell membrane | Cell wall |
|---|---|
| It is selectively permeable and allows only certain substances to enter or leave the cell. | It is generally freely permeable, allowing water and many dissolved substances to pass through it. |
(ii) RER and SER
| Rough Endoplasmic Reticulum (RER) | Smooth Endoplasmic Reticulum (SER) |
|---|---|
| Ribosomes are attached to its surface, giving it a rough appearance. | Ribosomes are absent from its surface, giving it a smooth appearance. |
(iii) Chloroplasts and chromoplasts
| Chloroplasts | Chromoplasts |
|---|---|
| They contain the green pigment chlorophyll. | They contain coloured pigments such as red, yellow and orange pigments. |
🟦 QUESTION 2
Two similar animal cells are placed in two different solutions:
- Cell X is placed in pure water.
- Cell Y is placed in a concentrated salt solution.
Cells are observed after some time. Cell X swells, and Cell Y shrinks. Which statement provides the correct explanation?
(i) Salt molecules moved into Cell Y, causing it to shrink.
(ii) Water moved into Cell X and more water moved out of Cell Y than the salt solution entered it.
(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
(iv) Solute movement caused osmosis in both cells.
🟩 ANSWER
Correct option: (iii)
Water moved into Cell X and moved out of Cell Y through the cell membrane.
Pure water is hypotonic compared with the contents of Cell X. Therefore, water enters Cell X by osmosis, causing it to swell.
The concentrated salt solution is hypertonic compared with Cell Y. Therefore, water moves out of Cell Y by osmosis, causing it to shrink.
🟦 QUESTION 3
Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled from (a) to (g) and match them with their functions:
- Controlling all activities of a cell
- Site of cellular respiration
- Storage organelle that also provides rigidity
- Separates cell contents from the surroundings
- Provides structural rigidity
- Packs and stores materials received from the ER
- Helps in manufacturing food
🟩 ANSWER
| Label | Cell part | Function |
|---|---|---|
| (a) | Mitochondrion | Site of cellular respiration |
| (b) | Nucleus | Controls all activities of the cell |
| (c) | Golgi apparatus | Packs and stores materials received from the ER |
| (d) | Chloroplast | Helps in manufacturing food |
| (e) | Cell wall | Provides structural rigidity |
| (f) | Cell membrane | Separates cell contents from the surroundings |
| (g) | Vacuole | Stores materials and provides rigidity |
🟦 QUESTION 4
Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories?
| Option | Present in plant cells | Absent in animal cells |
|---|---|---|
| (i) | Leucoplast | Cell wall |
| (ii) | Mitochondria | Ribosome |
| (iii) | Cell wall | Golgi apparatus |
| (iv) | Lysosome | Endoplasmic reticulum |
🟩 ANSWER
Correct option: (i) Leucoplast and cell wall
Leucoplasts are present in plant cells, especially in non-green storage parts such as roots and tubers.
The cell wall is present in plant cells but absent in animal cells.
The other options are incorrect because mitochondria, ribosomes, Golgi apparatus and endoplasmic reticulum are also present in animal cells.
🟦 QUESTION 5
Two students, Renu and Rohit, were discussing plastids. Renu said that all parts of plants, including roots, contain plastids. Rohit disagreed and said that plastids are absent in roots because roots are underground and do not perform photosynthesis. Who is correct? Justify your answer.
🟩 ANSWER
Renu is correct.
Roots generally do not contain chloroplasts because they remain underground and do not receive sufficient sunlight.
However, root cells contain colourless plastids called leucoplasts.
Leucoplasts store:
- Starch
- Oils
- Proteins
Therefore, plastids are present in roots mainly in the form of leucoplasts.
🟦 QUESTION 6
Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two organelles are structurally and functionally similar to and different from each other.
🟩 ANSWER
Similarities
- Both are surrounded by a double membrane.
- Both contain their own DNA and ribosomes.
- Both can synthesise some of their own proteins.
- Both are involved in energy conversion.
- Both are called semi-autonomous organelles.
Differences
| Mitochondria | Chloroplasts |
|---|---|
| Present in plant and animal cells. | Mainly present in green plant cells. |
| Carry out cellular respiration. | Carry out photosynthesis. |
| Break down food to release energy. | Use sunlight to manufacture food. |
| Produce energy in the form of ATP. | Convert light energy into chemical energy. |
| Inner membrane forms folds called cristae. | Contain chlorophyll-bearing structures arranged into grana. |
| Do not contain chlorophyll. | Contain chlorophyll. |
🟦 QUESTION 7
Which of the following pairs of cell organelles contains DNA?
(i) Chloroplasts and ribosomes
(ii) Mitochondria and nucleus
(iii) Golgi bodies and ribosomes
(iv) Nucleus and lysosomes
🟩 ANSWER
Correct option: (ii) Mitochondria and nucleus
The nucleus contains chromosomes made up of DNA and proteins.
Mitochondria also contain a small amount of their own DNA.
Ribosomes, Golgi bodies and lysosomes do not contain DNA.
🟦 QUESTION 8
A researcher took two carrots of similar size. She placed one carrot in plain water and the other in concentrated salt solution. After 24 hours, she recorded her observations.
(i) What hypothesis does she want to test?
🟩 ANSWER
She wants to test whether water moves into or out of carrot cells by osmosis, depending on the concentration of the surrounding solution.
She also wants to observe how osmosis affects the texture and firmness of the carrot.
(ii) What improvements would you suggest for this experiment?
🟩 ANSWER
The experiment can be improved by:
- Using carrots of equal size, thickness and mass.
- Measuring their initial and final mass or length.
- Using equal volumes of plain water and salt solution.
- Keeping the temperature the same.
- Keeping the duration of the experiment the same.
- Repeating the experiment for reliable results.
(iii) Why does the carrot in plain water remain stiff and crunchy, while the carrot in concentrated salt solution becomes rubbery and limp?
🟩 ANSWER
Plain water is hypotonic compared with carrot cells. Water enters the cells by endosmosis, making them turgid. Therefore, the carrot remains stiff and crunchy.
The concentrated salt solution is hypertonic. Water moves out of the carrot cells by exosmosis. The cells lose turgidity, causing the carrot to become rubbery and limp.
🟦 QUESTION 9
Indicate the presence or absence of the following structures in bacterial and animal cells:
- Chromosome
- Nucleus
- Mitochondria
- Golgi complex
- Chromoplasts
🟩 ANSWER
| Structure | Bacterial cell | Animal cell |
|---|---|---|
| Chromosome | Present | Present |
| Nucleus | Absent | Present |
| Mitochondria | Absent | Present |
| Golgi complex | Absent | Present |
| Chromoplasts | Absent | Absent |
In a bacterial cell, the chromosome is present in a region called the nucleoid. It is not enclosed within a nuclear membrane.
🟦 QUESTION 10
Take four peeled potato halves and scoop them out to make potato cups. One cup should be made from a boiled potato. Place each potato cup in a beaker containing water.
- Keep Cup A empty.
- Add one teaspoon of sugar to Cup B.
- Add one teaspoon of salt to Cup C.
- Add one teaspoon of sugar to the boiled potato Cup D.
(i) Why does water gather in Cups B and C?
🟩 ANSWER
Cup B contains sugar and Cup C contains salt. These substances form concentrated solutions inside the potato cups.
Water from the beaker moves through the selectively permeable membranes of living potato cells into the hollow portions by osmosis.
Therefore, water gathers in Cups B and C.
(ii) Why is Cup A necessary?
🟩 ANSWER
Cup A acts as a control setup.
It contains no sugar or salt, so no concentration difference is created.
It shows that water collects in Cups B and C because of the dissolved substances and osmosis.
(iii) Why does water not gather in Cups A and D?
🟩 ANSWER
Cup A: It contains no sugar or salt. Therefore, no concentration gradient is produced.
Cup D: It is made from boiled potato. Boiling destroys the cell membranes. Since a selectively permeable membrane is required for osmosis, water does not gather in Cup D.
🟦 QUESTION 11
Identify the pair that incorrectly matches the cell organelle with its function:
(i) Ribosome — Protein synthesis
(ii) SER — Lipid and cellulose synthesis
(iii) Lysosome — Digestion of foreign agents
🟩 ANSWER
Incorrect pair: (ii) SER — Lipid and cellulose synthesis
The Smooth Endoplasmic Reticulum synthesises lipids and certain hormones, but it does not synthesise cellulose.
The other pairs are correct:
- Ribosome — Protein synthesis
- Lysosome — Digestion of foreign materials
🟦 QUESTION 12
What outcome do you expect if all the mitochondria are removed from a eukaryotic cell?
🟩 ANSWER
Mitochondria carry out cellular respiration and produce energy in the form of ATP.
If all mitochondria are removed:
- Aerobic respiration will stop.
- ATP production will decrease greatly.
- The cell will not receive sufficient energy.
- Growth, repair and transport will be affected.
- The cell will eventually become non-functional and die.
🟦 QUESTION 13
Which phenomenon inhibits the formation of tumours in the human body? Can plants also develop tumours? Explain.
🟩 ANSWER
The phenomenon that inhibits tumour formation is called contact inhibition.
Normal animal cells stop dividing when they come into contact with neighbouring cells.
Cancer cells lose contact inhibition and continue dividing uncontrollably, forming tumours.
Yes, plants can also develop tumour-like growths called galls. These may be caused by microorganisms, genetic changes or uncontrolled cell division.
Plant tumours usually remain localised because plant cells are fixed in position by rigid cell walls.
🟦 QUESTION 14
The cell membrane is made up of proteins and lipids. Which cell organelles help in the synthesis of the cell membrane? Write the path of these compounds from their site of synthesis to the cell membrane and show it through a labelled diagram.
🟩 ANSWER
The following organelles are involved:
- Ribosomes on RER: synthesise membrane proteins.
- Smooth Endoplasmic Reticulum: synthesises membrane lipids.
- Golgi apparatus: modifies, sorts and packages these materials.
- Transport vesicles: carry them to the cell membrane.
Pathway of proteins
Ribosomes on RER
↓
Membrane proteins
↓
Transport vesicles
↓
Golgi apparatus
↓
Modification and packaging
↓
Golgi vesicles
↓
Cell membrane
Pathway of lipids
Smooth Endoplasmic Reticulum
↓
Membrane lipids
↓
Transport vesicles
↓
Golgi apparatus
↓
Golgi vesicles
↓
Cell membrane
Thus, the endoplasmic reticulum, ribosomes and Golgi apparatus work together in the formation and maintenance of the cell membrane.
🟦 QUESTION 15
What would happen if gametes were formed by mitotic divisions?
🟩 ANSWER
Mitosis does not reduce the chromosome number. Therefore, gametes formed by mitosis would contain the complete diploid number of chromosomes.
During fertilisation, two diploid gametes would fuse and form a zygote with twice the normal chromosome number.
Example in humans:
- Normal gamete formed by meiosis = 23 chromosomes
- Gamete formed by mitosis = 46 chromosomes
- Zygote formed after fertilisation = 92 chromosomes
The chromosome number would continue doubling in successive generations.
Genetic variation would also be reduced because mitosis produces genetically similar cells.
Therefore, normal sexual reproduction and development would be disturbed.
🟦 QUESTION 16
A farmer, Deepa, had a large harvest of amla and lemons but could sell only one-fourth of the produce. She prepared pickles, murabbas and sharbat by adding salt, sugar or jaggery and stored them in glass bottles.
(i) Which scientific concept has been applied?
🟩 ANSWER
The farmer has applied the concepts of osmosis and plasmolysis.
High concentrations of salt or sugar create a hypertonic environment around microorganisms and remove water from their cells.
(ii) How do high concentrations of salt and sugar prevent the growth of bacteria and fungi?
🟩 ANSWER
Salt and sugar create a hypertonic environment outside the cells of bacteria and fungi.
Water moves out of these microorganisms by osmosis.
As a result:
- Their cells lose water.
- Their cytoplasm shrinks.
- Their metabolic activities slow down or stop.
- They cannot grow and reproduce properly.
Therefore, food remains preserved for a longer time.
(iii) Suggest a healthy food-preservation recipe.
🟩 ANSWER
Healthy low-oil amla pickle
- Wash and lightly steam fresh amla.
- Separate the segments and dry them.
- Add turmeric, mustard seeds, fennel and a controlled amount of salt.
- Add lemon juice.
- Add a small amount of mustard oil.
- Store it in a clean, sterilised glass jar.
- Refrigerate after opening.
(iv) What scientific values are addressed in this case?
🟩 ANSWER
The scientific values shown are:
- Application of science in daily life
- Logical thinking
- Innovation and problem-solving
- Reduction of food wastage
- Sustainable use of farm produce
- Food security
- Entrepreneurship and self-reliance
- Support for the local economy
- Responsible use of natural resources