Question 1

Two students, Renu and Rohit, were having a discussion on the 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.

Accepted Answer

Renu is correct. Plastids are present in all parts of the plant including roots. Although roots do not perform photosynthesis, they contain leucoplasts, a type of plastid involved in storage of starch, oils, and proteins. Hence, plastids are not absent in roots; they just differ in type and function compared to chloroplasts found in green parts. — Plastids are a group of organelles found in plant cells. Chloroplasts are involved in photosynthesis and are found in green parts. Leucoplasts, which are non-pigmented plastids, are present in roots and are responsible for storage. Therefore, plastids are present in roots but not chloroplasts.

Question 2

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.

Accepted Answer

Similarities:
- Both have double membranes.
- Both contain their own DNA and ribosomes.
- Both are involved in energy transformations.
Differences:
- Mitochondria are the site of cellular respiration, producing ATP by breaking down glucose.
- Chloroplasts are the site of photosynthesis, converting light energy into chemical energy.
- Chloroplasts contain chlorophyll pigment; mitochondria do not.
- Mitochondria are found in almost all eukaryotic cells; chloroplasts are found only in plant cells and some protists. — Structurally, both organelles have double membranes and their own DNA, indicating semi-autonomous nature. Functionally, mitochondria generate energy by respiration, while chloroplasts capture light energy for photosynthesis. Their roles complement each other in plant cells.

Question 3

Which of the following pairs of cell organelles contains DNA?

(i) Chloroplasts, Ribosomes
(ii) Mitochondria, Nucleus
(iii) Golgi bodies, Ribosomes
(iv) Nucleus, Lysosomes

Accepted Answer

(ii) Mitochondria, Nucleus
Explanation: Both mitochondria and nucleus contain DNA. Chloroplasts also contain DNA but ribosomes do not. Golgi bodies and lysosomes do not contain DNA. — DNA is present in the nucleus and mitochondria (and also chloroplasts). Ribosomes are made of RNA and proteins but do not contain DNA. Golgi bodies and lysosomes are membrane-bound organelles without DNA.

Question 4

A researcher carried out an experiment in which she took two carrots of similar size. She placed one carrot in plain water and the other carrot in concentrated salt solution (Fig. 2.21). After 24 hours she recorded her observations.

(i) What hypothesis does she want to test through this experiment?
(ii) What would you suggest for the improvement of this experiment?
(iii) Why does the carrot in plain water stay stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp?

Accepted Answer

(i) Hypothesis: Water moves from a region of higher water potential to a region of lower water potential through a semi-permeable membrane (osmosis).

(ii) Improvement: Use more replicates for each condition, measure the change in weight or firmness quantitatively, and control temperature.

(iii) Explanation: The carrot in plain water gains water by osmosis, making it stiff and crunchy due to turgidity. The carrot in salt solution loses water to the solution (which has lower water potential), becoming limp and rubbery due to loss of turgor pressure. — Osmosis causes water to move into the carrot cells in pure water, increasing turgor pressure and firmness. In salt solution, water moves out of the cells, decreasing turgor pressure and causing limpness.

Question 5

Indicate the presence or absence of following structures in bacterial and animal cells:

Structures in a cell | Bacterial cell | Animal cell
Chromosome | ? | ?
Nucleus | ? | ?
Mitochondria | ? | ?
Golgi complex | ? | ?
Chromoplasts | ? | ?

Accepted Answer

Presence or absence:
- Chromosome: Present in both bacterial and animal cells.
- Nucleus: Absent in bacterial cells; present in animal cells.
- Mitochondria: Absent in bacterial cells; present in animal cells.
- Golgi complex: Absent in bacterial cells; present in animal cells.
- Chromoplasts: Absent in both bacterial and animal cells. — Bacteria are prokaryotes and lack membrane-bound organelles like nucleus, mitochondria, and Golgi complex. They have chromosomes but no nucleus. Chromoplasts are plastids found in plants, absent in bacteria and animals.

Question 6

Carry out the following experiment:

Take four 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 (Fig. 2.22). Now, set up the experiment as follows:

(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 four potato cups at least two hours and answer the following 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.

Accepted Answer

(i) Water gathers in Cups B and C because sugar and salt create a hypertonic solution inside the potato cups. Water moves from the beaker (higher water potential) into the cups (lower water potential) by osmosis.

(ii) Cup A is necessary as a control to show that water does not move when there is no solute inside the cup.

(iii) Water does not gather in Cup A because it is empty and there is no solute to create osmotic gradient. In Cup D, the potato is boiled, so its cells are dead and membranes are damaged, preventing osmosis. — Osmosis causes water to move towards higher solute concentration. Boiling destroys cell membranes, stopping osmotic movement. The control cup shows baseline condition without solute.

Question 7

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

Accepted Answer

(ii) SER — Lipid and cellulose synthesis is incorrect because SER (Smooth Endoplasmic Reticulum) is involved in lipid synthesis but not cellulose synthesis. Cellulose synthesis occurs in the cell wall.

Ribosomes synthesize proteins and lysosomes digest foreign agents. — SER synthesizes lipids and detoxifies substances but cellulose is synthesized outside the cell membrane by enzymes. Hence, the pairing of SER with cellulose synthesis is incorrect.

Question 8

What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?

Accepted Answer

If all mitochondria are removed, the cell will not be able to produce sufficient energy (ATP) through cellular respiration. This will lead to failure of energy-dependent processes and eventually cell death. — Mitochondria are the powerhouse of the cell, generating ATP by aerobic respiration. Without mitochondria, energy production ceases, impairing cell functions.

Question 9

Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.

Accepted Answer

Contact inhibition inhibits tumor formation in human body cells by stopping cell division when cells come into contact. Plants can also develop tumors, called galls, caused by infections or genetic mutations, but plant cells do not exhibit contact inhibition like animal cells. — In animals, contact inhibition prevents uncontrolled cell division. Loss of this leads to tumors. Plants develop tumors due to different mechanisms, often involving pathogens like Agrobacterium.

Question 10

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.

Accepted Answer

The Smooth Endoplasmic Reticulum (SER) synthesizes lipids, and ribosomes on Rough Endoplasmic Reticulum (RER) synthesize proteins. These compounds are transported via vesicles to the Golgi apparatus for modification and packaging. Finally, vesicles carry them to the cell membrane where they are incorporated.

Path: Ribosomes (protein synthesis) → RER → Transport vesicles → Golgi apparatus → Secretory vesicles → Cell membrane.

A labelled diagram should show nucleus, RER, SER, Golgi apparatus, vesicles, and cell membrane. — Lipids and proteins are synthesized in ER and ribosomes, processed in Golgi, and transported in vesicles to the membrane for assembly, maintaining membrane structure and function.

Question 11

What would happen if gametes are formed by mitotic divisions?

Accepted Answer

If gametes are formed by mitotic divisions, they would be diploid instead of haploid. This would lead to doubling of chromosome number in each generation after fertilization, disrupting genetic stability. — Mitosis produces genetically identical diploid cells. Gametes must be haploid to maintain chromosome number after fertilization. Meiosis reduces chromosome number by half.

Question 12

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 the 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 the 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 for food preservation.

(iv) What are the scientific values addressed in this case?

Accepted Answer

(i) The farmer applied the scientific concept of osmosis and preservation by creating hypertonic environments using salt and sugar to inhibit microbial growth.

(ii) High concentrations of salt and sugar reduce water availability by creating hypertonic conditions, causing microbial cells to lose water and become dehydrated, thus preventing their growth.

(iii) A healthy recipe could be preparing fruit murabba by boiling fruit pieces with jaggery and storing them in sterilized containers.

(iv) Scientific values include application of scientific knowledge for sustainability, reducing waste, food preservation, and promoting local economy. — Salt and sugar preservation works by osmosis, drawing water out of microbes. This traditional method is scientifically valid and helps reduce post-harvest losses.

Question 13

What is the limit of resolution of the human eye, and why can't cells be seen clearly without aid?

Accepted Answer

0.1 mm; cells are smaller than this limit — The limit of resolution of the human eye is about 0.1 mm, meaning two points closer than this appear as one. Since most cells are smaller than 0.1 mm, they cannot be seen clearly without magnification.

Question 14

Identify the structure labelled as the eyepiece in the diagram of a light microscope showing its parts: eyepiece, objective lens, stage, and coarse adjustment knob.

Accepted Answer

The top lens through which the observer looks — The eyepiece is the lens at the top of the microscope through which the observer views the magnified image. It usually has a magnifying power of 10X.

Question 15

Which of the following best explains why electron microscopes provide better resolution than light microscopes?

Accepted Answer

Electron beams have a much shorter wavelength than visible light — Electron microscopes use electron beams which have much shorter wavelengths than visible light, allowing them to resolve much smaller structures and provide higher magnification and resolution.

Cell: The Building Block of Life

Cell: The Building Block of Life — Study Notes

Cell: The Building Block of Life

2.1 How to Study Cells?

2.2 Structure of a Cell

Practice Questions — Cell: The Building Block of Life

All 13 Chapters in Exploration