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

Short Answer Type

Question 1. Why the cell called the structural & functional unit of life ?
Answer:
Structural unit: the body of every living organism is built from one or more cells. Just as bricks build a wall, cells build tissues, tissues build organs and organs build the organism.
Functional unit: every cell carries out the basic life activities by itself: it takes in food, respires, makes proteins, removes wastes and responds to its surroundings. The functions of a whole organism are the sum of the work done by its cells.
In simple words: A cell is the smallest part that is both a building block and a working unit of a living body.

Teacher's Note:
1. Answer in two parts, one for structure and one for function.
2. Mention that even a single-celled organism does all life activities within its one cell.

Teacher's Note:
1. Always give an example from both sides in a comparison.
2. A differentiated cell can sometimes return to the dividing state; that is called dedifferentiation.

Question 3. Cell shape differentiate according to their function explain.
Answer:
The shape of a cell suits the work it does:
1. Nerve cell: long and branched, so that it can carry messages over long distances.
2. Red blood cell: a round disc that is thin in the middle, which gives a large surface for carrying oxygen and lets it pass through narrow blood vessels.
3. Muscle cell: spindle-shaped, long and able to shorten, which helps the muscle to contract.
4. Cells of the alimentary canal: tall and column-like, which gives space for absorbing digested food.
5. Pigment cell: branched, so that pigment can spread over a large area of skin.
In simple words: Each kind of cell has the shape that helps it do its own job best.

Teacher's Note:
1. Pick 3 or 4 well-known examples and link each shape to a function.
2. Do not just list shapes; say why the shape is useful.

Question 4. If the organisation of a cell is destroyed due to some physical or chemical influence. What will happen ?
Answer:
A cell works because its parts (membrane, nucleus, organelles) are arranged in an orderly way and cooperate with one another.
If this organisation is destroyed, the cell can no longer carry out its life activities such as respiration, protein making and transport of materials. In addition, the lysosomes may burst and digest the cell. The cell loses its life, that is, it dies.
In simple words: When a cell's organisation is destroyed, it can no longer do its work and dies.

Teacher's Note:
1. Think of a factory whose machines are all broken: production stops.
2. Mention the role of lysosomes to score extra.

Teacher's Note:
1. Link the plastid with its colour: coloured, green, white.
2. Leucoplasts store food as starch, oil or protein.

Teacher's Note:
1. Give at least three differences for 2 marks.
2. The onion cell also has a large vacuole.

Question 7. How do substances like carbon dioxide (CO₂) and water (H₂O) move in and out of the cell ?
Answer:
Carbon dioxide (CO₂) moves by diffusion, from a region of higher concentration to a region of lower concentration. Cells make CO₂ in respiration, so it diffuses out.
Water (H₂O) moves by osmosis through the selectively permeable plasma membrane, from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution).
In simple words: Carbon dioxide moves by diffusion and water moves by osmosis.

Teacher's Note:
1. Both processes are passive: they need no energy.
2. Osmosis is a special kind of diffusion of water.

Question 8. How does amoeba obtain its food ?
Answer:
The amoeba is a single cell without a cell wall. It takes in food by endocytosis (phagocytosis).
It stretches out finger-like pseudopodia around the food particle and encloses it in a bag called a food vacuole. Lysosomal enzymes digest the food in this vacuole, the digested food passes into the cytoplasm and the undigested part is thrown out.
In simple words: Amoeba surrounds the food with its body and digests it inside a food vacuole.

Teacher's Note:
1. Name the process (phagocytosis) and describe it.
2. This is possible only because the membrane is flexible.

Question 9. Name the two organelles in a plant cell that contain their own genetic material and ribosomes.
Answer:
Mitochondria and chloroplasts. Both have their own circular DNA and 70S ribosomes, so they are semi-autonomous.
In simple words: Mitochondria and chloroplasts have DNA and ribosomes of their own.

Teacher's Note:
1. The same two organelles also have double membranes.
2. The 70S ribosomes are like those of bacteria.

Question 10. Who gave the cell theory ? What does it state ? Which organism is an exception of cell theory ?
Answer:
Who: M. J. Schleiden and Theodor Schwann gave the cell theory, and Rudolf Virchow expanded it.
It states:
1. All plants and animals are composed of cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells.
Exception: viruses, which are not made of cells, are the exception to the cell theory.
In simple words: The theory says living things are made of cells and cells come from cells; viruses are the exception.

Teacher's Note:
1. Give all three statements.
2. Viruses show life only inside a living host cell.

Teacher's Note:
1. Four points are enough for a full-mark answer.
2. Both are passive transport.

Question 12. Why plasma membrane is called selectively permeable membrane ?
Answer:
The plasma membrane lets some substances such as water, oxygen, carbon dioxide and nutrients pass through it, but it does not allow other substances to cross, or lets them cross only when special carrier proteins help.
Since it permits only selected materials to enter or leave the cell, it is called a selectively permeable membrane. This keeps the contents of the cell constant.
In simple words: It allows only chosen substances to pass in or out.

Teacher's Note:
1. Use the word 'selected' in your answer.
2. Cell wall, in contrast, is fully permeable.

Question 13. State any two functions of golgi body.
Answer:
1. It collects, modifies and packs substances made in the cell (secretion), and sends them out.
2. It forms lysosomes.
In simple words: Golgi body packages and secretes materials and forms lysosomes.

Teacher's Note:
1. Other functions: forming the acrosome of sperm and the cell plate.
2. It is the 'packaging and dispatch' department of the cell.

Question 14. State any two functions of golgi body.
Answer:
1. It forms the acrosome of the sperm.
2. It makes the material of the cell wall in plant cells and helps in forming the cell plate when the cell divides (the plasma membrane is also formed with its help).
In simple words: Golgi body forms the acrosome and the cell wall material.

Teacher's Note:
1. The question appears twice in the book, so a different pair of functions is given here.
2. Writing any two correct functions earns full marks.

Question 15. State the main functions of lysosomes ?
Answer:
1. They digest food and other material inside the cell (intracellular digestion).
2. They are the waste-disposal system of the cell.
3. They digest foreign material, such as bacteria, and worn-out cell parts.
4. They burst and digest the cell when it is damaged, so they are called suicide bags.
In simple words: Lysosomes digest and clean up inside the cell.

Teacher's Note:
1. Remember they hold hydrolase enzymes.
2. Give at least 3 functions.

Question 16. Write down name of the all parts of microscope.
Answer:
The parts of a compound microscope are:
1. Base, 2. Handle (arm), 3. Stage, 4. Stage clips, 5. Condenser, 6. Body tube (with eyepiece, draw tube and objectives), 7. Adjustment screws (coarse and fine) and 8. Reflecting mirror.

In simple words: A microscope has a base, arm, stage with clips, condenser, body tube with lenses, adjustment screws and a mirror.

Teacher's Note:
1. Learn the labelled diagram together with this list.
2. Eyepiece and objectives are the lenses.