CBSE Class 9 Science Advanced Biology Fundamental Unit of Life Long Answer Questions Set 01

Long Answer Type (4 Marks)

Question 1. Why do plant cells possess large sized vacuole ?
Answer:
A mature plant cell has one large central vacuole, which can take up about 90% of the cell volume, because:
1. It stores water, sugars, salts and amino acids that the plant may need later.
2. It keeps the cell turgid. Water in the vacuole presses on the cytoplasm and the wall, which gives support and firmness to the plant.
3. It maintains the osmotic pressure of the cell.
4. Plants have no excretory organs, so toxic waste products are stored in the vacuole.
5. It holds coloured pigments such as anthocyanins, which colour many flowers and fruits.
In simple words: The large vacuole is the plant cell's store of water and wastes and also keeps it firm.

Teacher's Note:
1. Remember: storage, turgidity, osmosis, waste and pigments.
2. In animal cells the vacuoles are small and many.

Question 2. How are chromatin, chromatid and chromosomes related to each other ?
Answer:
Chromatin is the thin, tangled network of long threads of DNA and histone proteins seen in the nucleus of a cell that is not dividing.
When the cell is going to divide, the chromatin threads coil, shorten and thicken into rod-like chromosomes. After the DNA has been copied, each chromosome is made of two identical halves called chromatids, which are joined at one point, the centromere.
During division the chromatids separate and each becomes a chromosome of one daughter cell.
So: chromatin (thread form) coils up to form chromosomes, and each chromosome has two chromatids.
In simple words: Chromatin is the loose thread form of DNA, chromosomes are its tightly coiled form, and chromatids are the two halves of a chromosome.

Teacher's Note:
1. Draw a small sketch of an X-shaped chromosome to support your answer.
2. Chromatin and chromosomes are the same material in two different states.

Question 3. 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) The cell has more water than its surroundings, so the surrounding solution is hypertonic. Water moves out of the cell by exosmosis. An animal cell shrinks (crenation) and a plant cell shrinks away from its wall; this is called plasmolysis.
(b) The cell has less water than its surroundings, so the surrounding solution is hypotonic. Water enters the cell by endosmosis and the cell swells. An animal cell may burst (lyse), while a plant cell becomes firm or turgid because its cell wall stops it from bursting.
(c) The solution is isotonic. Water moves in and out at the same rate, so there is no net movement and the cell stays the same size.

In simple words: Water leaves a cell in a stronger solution, enters it in a weaker solution, and the cell is unchanged in an equal solution.

Teacher's Note:
1. First decide whether the outside solution is hypertonic, hypotonic or isotonic.
2. Write separately what happens to an animal cell and a plant cell.

Question 4. How can prepare microscopic slide explain.
Answer:
A temporary slide is prepared as follows:
1. Take a clean glass slide.
2. Put a drop of water in the middle of the slide with a dropper.
3. Place the specimen in the drop with the help of a brush.
4. If the specimen is transparent, stain it first with a suitable stain.
5. Hold a coverslip so that its edge touches the edge of the drop, and lower it slowly and gently, so that no air bubble is trapped.
6. Soak up any extra water around the coverslip with blotting paper. The slide must be clean and dry. It is now ready to be observed.

In simple words: Place the specimen in a drop of water on a slide and cover it with a coverslip.

Teacher's Note:
1. Follow the order of the steps and mention the dropper, brush and blotting paper.
2. A slow lowering of the coverslip avoids air bubbles.

Very Long Answer Type (5 Marks)

Question 5. Draw a neat labelled diagram of an animal cell.
Answer:

An animal cell has a plasma membrane (no cell wall), a nucleus with a nucleolus, cytoplasm with organelles such as mitochondria, rough and smooth endoplasmic reticulum, Golgi complex, lysosomes and free ribosomes, and a centriole near the nucleus. There is no large central vacuole and there are no plastids.
In simple words: An animal cell is bounded by a plasma membrane and has a nucleus, organelles and centrioles but no wall or plastids.

Teacher's Note:
1. Draw with a sharp pencil and label with straight lines.
2. Use only the labels you are sure about; marks are given for labelling.

Teacher's Note:
1. Label the nuclear envelope, pore, nucleoplasm, chromatin and nucleolus.
2. Give at least 3 differences for full marks.

Teacher's Note:
1. A table is the best way to answer the 'differentiate' part.
2. For the second part, name both lipid and protein making.

Question 8. Draw a neat and labelled diagram of nucleus. State its main functions.
Answer:

Main functions of the nucleus:
1. It controls all the metabolic activities of the cell.
2. It brings about growth by directing the making of structural proteins.
3. It takes part in the formation of ribosomes.
4. It regulates the cell cycle.
5. It holds the hereditary information (DNA) and passes it from one generation to the next.
In simple words: The nucleus is the control centre of the cell.

Teacher's Note:
1. Label at least nuclear envelope, nuclear pore, nucleoplasm, chromatin and nucleolus.
2. Five functions are given; write at least three.

Question 9. Describe the types of endoplasmic reticulum and draw necessary figure. Give its main functions also.
Answer:

Types of ER:
1. Rough ER (RER): ribosomes are attached to its surface. It is made of cisternae and vesicles, lies near the nucleus and makes proteins.
2. Smooth ER (SER): has no ribosomes. It is made mostly of tubules, lies near the cell membrane and makes lipids and steroids.
Main functions:
1. It increases the surface area for the metabolic activities of the cell.
2. It gives internal support to the cytoplasm.
3. It transports substances inside the cell.
4. The rough ER makes proteins, and the smooth ER makes lipids and sex hormones and takes part in detoxification.
In simple words: ER is of two kinds: rough, which makes proteins, and smooth, which makes lipids.

Teacher's Note:
1. Draw the cisternae, vesicles and tubules and mark the ribosomes.
2. Link each type with its function.