CBSE Class 9 Biology The Fundamental Unit of Life MCQs Set 09

Answer: (a) Ribosomes

Explanation:
1. Ribosomes are too small to be seen with a light microscope, and were seen only with the electron microscope.
2. Mitochondria, chloroplasts and leucoplasts can be seen with a light microscope.

Teacher's Note:
1. Ribosomes are about 20 nm in size.
2. The electron microscope gives a much higher resolution.

Answer: (b) 75-100 Å

Explanation:
1. The plasma membrane is very thin, about 75-100 Å (7.5 to 10 nm).

Teacher's Note:
1. 1 Å is 10^-10 m.
2. It is visible only under the electron microscope.

Answer: (b) Active transport requires energy whereas passive transport follows the concentration gradient

Explanation:
1. Active transport moves substances against the concentration gradient using energy (ATP).
2. Passive transport follows the gradient and needs no energy.

Teacher's Note:
1. Diffusion and osmosis are passive.
2. Active transport is carried out by carrier proteins (pumps).

Answer: (a) Carbohydrate portion

Explanation:
1. The sugar chains (carbohydrate part) projecting from the cell surface act as recognition sites.

Teacher's Note:
1. Glycoproteins are proteins with attached carbohydrate chains.
2. They help cells identify each other.

Answer: (d) Some proteins embedded and some on the surfaces

Explanation:
1. In the fluid mosaic model (Singer and Nicolson) some proteins lie on the surface (peripheral) and others are embedded in the bilayer (integral).

Teacher's Note:
1. The lipids and proteins can move sideways, so the membrane is fluid.
2. The proteins form a mosaic pattern.

Answer: (a) Concentration of water molecules inside and outside the cell

Explanation:
1. Water moves from the region of higher water concentration to the region of lower water concentration.

Teacher's Note:
1. Osmosis is diffusion of water through a semi-permeable membrane.
2. Solutes decide how much free water is present.

Answer: (d) Cell Q is a bacterium

Explanation:
1. Both cells took in water, so neither cell sap is isotonic to pure water.
2. Q did not burst, so it has a cell wall, which fits a bacterium and not an animal cell like P.

Teacher's Note:
1. Animal cells lack a cell wall and burst in a hypotonic solution.
2. A cell wall stops the cell from bursting.

Answer: (c) Hypertonic

Explanation:
1. A solution with more solute than the cell is hypertonic to it, and water leaves the cell.

Teacher's Note:
1. In a hypotonic solution the cell swells.
2. In an isotonic solution there is no net movement.

Answer: (a) Pinocytosis

Explanation:
1. Pinocytosis is the intake of fluid droplets by the cell membrane, called cell drinking.

Teacher's Note:
1. Phagocytosis is cell eating.
2. Both are types of endocytosis.

Answer: (c) Pectin

Explanation:
1. The middle lamella between two plant cells is made of calcium and magnesium pectate.

Teacher's Note:
1. It cements neighbouring cells together.
2. It is the first layer to form after cell division.

Answer: (b) Solubilisation of pectate of the middle lamella

Explanation:
1. During ripening the pectate of the middle lamella dissolves, so cells separate from each other and the fruit becomes soft.

Teacher's Note:
1. Pectic enzymes cause this softening.
2. Starch to sugar conversion makes the fruit sweet.

Answer: (b) Nucleolus

Explanation:
1. The nucleolus is not bound by a membrane.
2. Lysosomes, mitochondria and plastids are all membrane bound.

Teacher's Note:
1. The nucleolus lies inside the nucleus.
2. It makes ribosomal RNA.

Answer: (b) Nucleus

Explanation:
1. The nucleus contains the nucleolus and the chromosomes, which in turn carry genes.

Teacher's Note:
1. Genes are parts of chromosomes.
2. The nucleus is the largest of these structures.

Answer: (d) Bacterial cell

Explanation:
1. Bacteria have no true nucleus, and their DNA lies in an irregular region called the nucleoid.

Teacher's Note:
1. Plant, animal and green algal cells have a true nucleus.
2. Prokaryotes have a nucleoid.

Answer: (b) Animals

Explanation:
1. Centrioles are found in animal cells and help in cell division.
2. Higher green plants, bacteria and cyanobacteria lack them.

Teacher's Note:
1. Centrosome has two centrioles.
2. They form the spindle in animal cells.

Answer: (d) Cell division

Explanation:
1. Microtubules form the spindle fibres, so they take part in cell division.

Teacher's Note:
1. They also form cilia and flagella.
2. They give shape to the cell.

Answer: (d) Centrioles

Explanation:
1. Centrioles are usually present only in animal cells.
2. Vacuoles and the cell wall are prominent in plant cells, and the nucleus is in both.

Teacher's Note:
1. Plant cells have a large central vacuole.
2. Plant cells have a cell wall.

Answer: (a) Exported from the cell

Explanation:
1. Ribosomes on the rough ER make proteins that are mostly secreted (exported) from the cell.

Teacher's Note:
1. Rough ER is studded with ribosomes.
2. Proteins pass to the Golgi apparatus for packaging.

Answer: (d) SER

Explanation:
1. The smooth endoplasmic reticulum detoxifies drugs and poisons in liver cells.

Teacher's Note:
1. SER makes lipids and steroids.
2. Liver cells have abundant SER.

Answer: (c) RER

Explanation:
1. The rough endoplasmic reticulum has ribosomes on its surface and makes proteins and enzymes.

Teacher's Note:
1. SER has no ribosomes.
2. The Golgi complex modifies and packs them.

Answer: (d) Endoplasmic reticulum

Explanation:
1. Prokaryotes have DNA, a cell membrane and (usually) a cell wall, but no membrane-bound organelles such as the endoplasmic reticulum.

Teacher's Note:
1. Prokaryotes have only ribosomes as organelles.
2. The ER is found in eukaryotes.

Answer: (a) Germinating seeds

Explanation:
1. Germinating seeds need much energy for growth, so their cells have more mitochondria.

Teacher's Note:
1. Dormant and dry seeds are inactive.
2. Mitochondria produce ATP.

Answer: (c) Lysosome

Explanation:
1. Lysosomes show polymorphism: they occur as primary and secondary lysosomes, residual bodies and autophagic vacuoles.

Teacher's Note:
1. Their shape and size vary.
2. They contain digestive enzymes.

Answer: (d) All of the above

Explanation:
1. The Golgi apparatus modifies proteins, packs them into vesicles and sends them out of the cell.

Teacher's Note:
1. It is the packaging and dispatching centre.
2. It also forms lysosomes.

Answer: (a) Golgi apparatus

Explanation:
1. The acrosome of a sperm is formed from the Golgi apparatus.

Teacher's Note:
1. It contains enzymes that help to penetrate the egg.
2. The acrosome is a modified lysosome-like sac.

Answer: (d) ER

Explanation:
1. The endoplasmic reticulum forms a network of channels that carries materials within the cell.

Teacher's Note:
1. It acts as the intracellular transport system.
2. The ER links the nucleus with the plasma membrane.

Answer: (b) Lysosome

Explanation:
1. Lysosomes contain hydrolytic enzymes and digest macromolecules inside the cell.

Teacher's Note:
1. They are called suicide bags.
2. They work at acidic pH.

Answer: (b) Mitochondria

Explanation:
1. Mitochondria have their own DNA and ribosomes and can divide, so they are semi-autonomous.

Teacher's Note:
1. Chloroplasts are also semi-autonomous.
2. They make some of their own proteins.