Revise, Reflect, Refine
1. Differentiate between the following pairs of terms based on the clues given in parentheses:
(i) Cell membrane and Cell wall (Permeability)
| Basis | Cell Membrane | Cell Wall |
|---|---|---|
| Nature | Thin, living and flexible membrane | Thick, non-living and rigid covering |
| Permeability | Selectively permeable – allows only certain substances to pass | Freely permeable – allows most substances to pass |
| Presence | Present in all cells | Present mainly in plant cells |
| Function | Controls movement of materials in and out of the cell | Provides shape, support and protection |
(ii) RER and SER (Structure)
Basis | RER (Rough Endoplasmic Reticulum) | SER (Smooth Endoplasmic Reticulum) |
|---|---|---|
Surface | Ribosomes are present on the surface | Ribosomes are absent |
Appearance | Rough in appearance | Smooth in appearance |
Shape | Usually consists of flattened sacs | Usually tubular network |
Main Function | Helps in protein synthesis | Helps in fat and lipid synthesis |
(iii) Chloroplasts and Chromoplasts (Pigments)
| Basis | Chloroplasts | Chromoplasts |
|---|---|---|
| Pigment | Contain chlorophyll (green pigment) | Contain carotenoid pigments like yellow, orange or red |
| Colour | Green | Yellow, orange or red |
| Function | Perform photosynthesis | Give colour to fruits and flowers |
| Presence | Found mainly in green parts of plants | Found in coloured fruits and flowers |
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 for the above observations?
(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 in 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.
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3. Look at the diagram of a cell in Fig.2.20. Identify the parts labelled from (a) to (g) and correctly match them with their functions given below.
(i) Controlling all the activities of a cell.
(ii) Site of cellular respiration.
(iii) Storage organelle that also provides rigidity to the cell.
(iv) Separates the cell contents from surroundings.
(v) Provides structural rigidity to the cell.
(vi) Packs and stores materials received from ER.
(vii) Helps in manufacturing food.
| Label | Cell Part | Function |
|---|---|---|
| (a) | Mitochondria | Site of cellular respiration |
| (b) | Nucleus | Controls all activities of the cell |
| (c) | Golgi apparatus | Packs and stores materials received from ER |
| (d) | Cell wall | Provides structural rigidity to the cell |
| (e) | Cell membrane | Separates the cell contents from surroundings |
| (f) | Cytoplasm | Jelly-like substance where organelles are present |
| (g) | Vacuole | Storage organelle that also provides rigidity |
4. Which of the following option(s) of pairs of cell organelles are correctly placed under the given categories?
Option | Present in the plant cells | Absent in the animal cells |
|---|---|---|
(i) | Leucoplast | Cell wall |
(ii) | Mitochondria | Ribosome |
(iii) | Cell wall | Golgi apparatus |
(iv) | Lysosome | Endoplasmic reticulum |
(i) Leucoplast — Cell wall
- Leucoplasts are present in plant cells and absent in animal cells.
- Cell wall is present in plant cells but absent in animal cells.
The other options are incorrect because:
- Mitochondria and ribosomes are present in both plant and animal cells.
- Golgi apparatus is present in both plant and animal cells.
- Endoplasmic reticulum is also present in animal cells.
5. Two students, Renu and Rohit, were having a discussion on plastids.
Renu emphasised that all parts of the plants, even roots, contain plastids. However, Rohit did not agree with the statement and told her that plastids are absent in plant roots since the roots are underground and do not need to perform photosynthesis. Who is correct? Justify your answer.
Renu is correct.
Roots do contain plastids, but they usually contain leucoplasts instead of chloroplasts.
Types of plastids:
1. Chloroplasts – Green plastids for photosynthesis
2. Chromoplasts – Coloured plastids
3. Leucoplasts – Colourless plastids for food storage
Since roots are underground and do not perform photosynthesis, chloroplasts are absent. However, leucoplasts are present for storage of starch, oils and proteins.
Therefore, roots contain plastids in the form of leucoplasts.
6. Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two organelles are structurally and functionally similar to each other, and different from each other.
Similarities between Mitochondria and Chloroplasts
| Basis | Similarity |
|---|---|
| Membrane | Both are double membrane-bound organelles |
| DNA | Both contain their own DNA |
| Ribosomes | Both possess ribosomes |
| Nature | Both are semi-autonomous |
| Function | Both are involved in energy conversion |
Differences between Mitochondria and Chloroplasts
| Basis | Mitochondria | Chloroplast |
|---|---|---|
| Presence | Present in plant and animal cells | Present only in plant cells |
| Function | Site of cellular respiration | Site of photosynthesis |
| Pigment | Chlorophyll absent | Chlorophyll present |
| Colour | Colourless | Green |
| Energy Conversion | Converts food into ATP | Converts sunlight into chemical energy |
7. Which of the following pairs of cell organelles contains DNA?
(i) Chloroplasts, Ribosomes
(ii) Mitochondria, Nucleus
(iii) Golgi bodies, Ribosomes
(iv) Vacuoles, Lysosomes
Correct: (ii) Mitochondria, Nucleus
Explanation:
Both mitochondria and nucleus contain DNA. Chloroplasts also contain DNA, but ribosomes do not.
8. A researcher carried out an experiment in which she cut two carrot pieces of similar size. She placed one carrot in plain water and the other carrot in concentrated salt solution. After 24 hours she recorded her observations.
(i) What hypothesis does she want to test through this experiment?
(ii) What could you suggest for the improvement of this experiment?
(iii) Why does the carrot in plain water become stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp?l
(i) Hypothesis
The experiment tests the process of osmosis and the movement of water across cell membranes.
(ii) Improvements
Use carrot pieces of equal size and weight.
Maintain equal temperature conditions.
Use equal quantities of solution.
Repeat the experiment for accuracy.
(iii) Explanation
Carrot in plain water:
Water enters the carrot cells through osmosis making them turgid and firm.
Carrot in concentrated salt solution:
Water moves out of the carrot cells causing plasmolysis, making them soft and limp.
9. Indicate the presence or absence of the following structures in bacterial and animal cells.
- Chromosome
- Nucleus
- Mitochondria
- Golgi complex
- Chromoplasts
| Structure | Bacterial Cell | Animal Cell |
|---|---|---|
| Chromosome | Present | Present |
| Nucleus | Absent | Present |
| Mitochondria | Absent | Present |
| Golgi complex | Absent | Present |
| Chromoplasts | Absent | Absent |
10. Carry out the following experiment:
Cut peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Place each of the potato cups in a beaker containing water.
Set up:
- (a) Keep Cup A empty.
- (b) Add one teaspoon sugar in Cup B.
- (c) Add one teaspoon salt in Cup C.
- (d) Add one teaspoon sugar in the boiled potato in Cup D.
Observe the potato cups after at least two hours and answer the questions:
(i) Explain why water gathers in the hollowed portion of Cup B and Cup C.
(ii) Why is Cup A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed portions of Cups A and D.
(i) Water gathers in Cups B and C because:
Sugar and salt create a concentrated solution inside the potato cups. Water moves from the surrounding beaker into the cups through osmosis.
(ii) Cup A is necessary because:
Cup A acts as the control setup. It helps compare the results with the other cups.
(iii) Explanation
Cup A:
No concentration difference exists, so osmosis does not occur.
Cup D:
Boiling destroys the selectively permeable membrane of potato cells, so osmosis cannot occur.
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
Incorrect Pair:
(ii) SER – Lipid and cellulose synthesis
Explanation:
SER helps in synthesis of lipids and fats, but not cellulose.
12. What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?
If all mitochondria are removed:
- Cellular respiration will stop.
- ATP production will stop.
- The cell will not get energy for life processes.
- Eventually, the cell will die.
13. Which phenomenon inhibits the formation of tumours in the human body? Can plants also develop tumours? Explain.
Phenomenon:
Controlled cell division prevents tumour formation.
Can plants develop tumours?
Yes, plants can also develop tumours due to uncontrolled cell growth caused by infections such as Agrobacterium tumefaciens.
14. The cell membrane of a cell is made up of proteins and lipids. Which cell organelles help in the synthesis of cell membrane? Write the path of these compounds from their site of synthesis to the cell membrane and show this through a labelled diagram.
Organelles involved:
Rough Endoplasmic Reticulum (RER) synthesizes proteins.
Smooth Endoplasmic Reticulum (SER) synthesizes lipids.
Pathway:
Proteins:
RER → Golgi apparatus → Vesicles → Cell membrane
Lipids:
SER → Golgi apparatus → Vesicles → Cell membrane
15. What would happen if gametes are formed by mitotic divisions?
If gametes are formed by mitosis:
- Gametes would contain the same chromosome number as body cells.
- After fertilization, chromosome number would double in every generation.
- This would disturb genetic balance in organisms.
Therefore, gametes are formed by meiosis.
16. A farmer, Deepa, was very happy with the harvest of amla (Indian Gooseberry) and lemons on her farm. However, she could sell only one-fourth of the produce in the local market. Recognising that a significant amount of produce may be lost post-harvest, she employed a traditional yet scientifically sound method to extend the shelf life of amla and lemons. She turned perishable produce into profitable products, such as pickles and sharbat. She used the excess produce to prepare pickles, murabbas and sharbat by adding appropriate amounts of salt, sugar or jaggery to small pieces of fruit and their juices. These were then stored in small glass bottles for sale, helping her prevent wastage of post-harvest produce. This shift from farming to agro-processing would strengthen food security and boost the local economy, creating a sustainable model that cuts waste while increasing her income. Based on the above passage answer the following questions:
(i) Which scientific concept has the farmer applied in preservation of the farm produce?
(ii) How does the addition of high concentrations of salt and sugar create an environment that prevents the growth of spoilage-causing bacteria and fungi?
(iii) Suggest a healthy recipe of this kind of food preservation.
(iv) What are the scientific values addressed in this case?
(i) Scientific concept
The farmer applied the concept of food preservation using osmosis.
(ii) Explanation
High concentrations of salt and sugar remove water from bacteria and fungi through osmosis. Due to water loss, microorganisms shrink and cannot grow or reproduce.
(iii) Healthy recipes
Lemon pickle
Amla murabba
Mango pickle
Fruit jam
(iv) Scientific values
Prevention of food wastage
Sustainable use of resources
Scientific thinking
Entrepreneurship
Food security
Economic development