CBSE Class 10 Science Life Processes Worksheet Set 07

Answer: Alveoli (air sacs).

Teacher's Note:
1. Alveoli have very thin walls and are surrounded by capillaries.
2. Gas exchange between air and blood occurs here.

Answer: Digestive enzymes break food molecules down by adding water (hydrolysis).

Teacher's Note:
1. For example, amylase breaks starch into sugars using water.
2. Enzymes are biological catalysts.

Answer: Food is carried through the phloem from the leaves (source) to storage organs and growing parts (sink).

Teacher's Note:
1. Translocation in phloem needs energy from ATP.
2. It is bi-directional, unlike water movement in xylem.

Answer: Bile contains salts that emulsify large fat globules into tiny droplets, increasing the surface area for lipase. It also makes the food from the stomach alkaline so pancreatic enzymes can work.

Teacher's Note:
1. Bile is made in the liver and stored in the gall bladder.
2. Emulsification is physical, not chemical, breakdown.

Answer: It is selectively reabsorbed into the blood by the capillaries around the nephron tubule, so normally no glucose appears in urine.

Teacher's Note:
1. Useful substances like amino acids and salts are also reabsorbed.
2. Amount of water reabsorbed depends on how much excess water is in the body.

Answer: Plants absorb nitrogen as nitrates and nitrites (formed by nitrogen-fixing bacteria from atmospheric nitrogen); animals obtain it as proteins from plants or other animals.

Teacher's Note:
1. Atmospheric nitrogen cannot be used directly by most organisms.
2. Rhizobium in legume roots fixes nitrogen.

Answer: At night there is no photosynthesis, but the tree still respires, taking in oxygen and releasing CO₂. The oxygen available to us under the tree falls.

Teacher's Note:
1. Photosynthesis needs light, respiration goes on continuously.
2. The effect is small in open space but is a common caution.

Answer: The sinoatrial (SA) node in the right atrium. It generates the electrical impulses that start each heartbeat and set its rate.

Teacher's Note:
1. Artificial pacemakers do the same job when the SA node fails.
2. The heart is made of cardiac muscle.

Answer: The plant in light will live longer, because it photosynthesises and produces oxygen, which it can use for respiration. The plant in the dark cannot make oxygen and soon dies.

Teacher's Note:
1. Respiration needs oxygen even in plants.
2. Photosynthesis releases O₂ as a by-product.

Answer: Leaves are broad and thin with a large surface area to absorb light; they contain many chloroplasts in palisade cells; stomata allow CO₂ in and O₂ out; veins supply water and carry away food; air spaces in spongy cells aid gas exchange.

Teacher's Note:
1. Adaptation means a structure suited to its function.
2. Guard cells control the opening of stomata.

Answer: The amount of dissolved oxygen in water is much lower than the amount of oxygen in air. Aquatic animals must therefore pass more water over their gills to get enough oxygen.

Teacher's Note:
1. Air has about 21% oxygen.
2. Fish take in water through the mouth and pass it over gills.

Answer: Incomplete combustion of coal in a closed room produces carbon monoxide. CO combines with haemoglobin more strongly than oxygen does, so blood cannot carry oxygen and the people die.

Teacher's Note:
1. Keep rooms ventilated when burning fuel.
2. CO is colourless and odourless.

Answer: (a) To reduce water loss by transpiration.
(b) Salivary amylase turns starch into sugar (maltose).
(c) It releases insulin and glucagon into blood and pancreatic juice into the small intestine.
(d) Most water and useful substances are selectively reabsorbed.
(e) Root pressure, caused by active uptake of ions into the roots.

Teacher's Note:
1. At night stomata are mostly closed, so transpiration pull is weak.
2. Root pressure helps in pushing water in small plants and at night.

Answer: (i) Light intensity, carbon dioxide concentration, temperature and water availability.
(ii) (a) Decreases because of less light. (b) Decreases because of water shortage and closed stomata. (c) Increases because minerals support growth of leaves and chlorophyll. (d) Decreases because less CO₂ enters.

Teacher's Note:
1. Photosynthesis uses CO₂, water and light to form glucose.
2. A factor in short supply limits the rate.

Answer: Lymph is a colourless fluid that leaks from blood capillaries into the tissue spaces; it has fewer RBCs and proteins than blood, but contains lymphocytes. It flows from the tissues towards the heart.
Functions: carries digested and absorbed fat from the intestine, and helps in defence by destroying germs.

Teacher's Note:
1. Lymph vessels finally join the veins.
2. Lymph nodes help in fighting infection.