Page 95
1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
Answer:
In multicellular organisms, all the body cells are not in direct contact with the surrounding environment. So, every cell of the body will not get enough oxygen by the process of diffusion from the environment.
2. What criteria do we use to decide whether something is alive?
Answer:
Growth, reproduction, metabolism, consciousness, etc.
3. What are outside raw materials used by an organism?
Answer:
Organisms use organic molecules as raw material. Heterotrophs use food, and autotrophs use CO2, minerals, and water. Organisms receive oxygen for respiration.
4. What processes would you consider essential for maintaining life?
Answer:
Nutrition, respiration, transportation, excretion, etc.
Page 101
1. What are the differences between autotrophic nutrition and heterotrophic nutrition?
Answer:
- Autotrophic nutrition: Organisms synthesize their own food and do not depend on other organisms. They use simple inorganic materials and synthesize their food in the presence of sunlight. E.g., all green plants.
- Heterotrophic nutrition: Organisms cannot synthesize their own food and depend on other organisms for their food. E.g., all animals, most bacteria, and fungi.
2. Where do plants get each of the raw materials required for photosynthesis?
Answer:
- Carbon dioxide: Absorbed from the environment/atmosphere through stomata.
- Water: Absorbed from the soil through roots and transported to leaves.
- Sunlight: From the sun.
- Chlorophyll: Present in chloroplasts found in green leaves.
3. What is the role of the acid in our stomach?
Answer:
- To make an acidic medium which is necessary for the activation of the enzyme pepsin.
- To kill bacteria present in the food.
4. What is the function of digestive enzymes?
Answer:
Digestive enzymes break down complex molecules in the food into smaller, simpler molecules so that they can be absorbed by the intestinal wall.
5. How is the small intestine designed to absorb digested food?
Answer:
The small intestine is very long and highly coiled. Also, its inner lining has numerous finger-like structures called villi. All these features increase the surface area for maximum absorption of digested food. The villi have numerous blood vessels which take the absorbed food.
Page 105
1. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
Answer:
Aquatic organisms use oxygen dissolved in surrounding water, where the concentration of dissolved oxygen is very low, so their breathing rate is very high. Terrestrial organisms get oxygen from the oxygen-rich atmosphere, so they have a lower breathing rate than aquatic organisms.
2. What are the different ways in which glucose is oxidised to provide energy in various organisms?
Answer:
In all organisms, glucose (6-carbon molecule) is broken down, yielding pyruvate (3-carbon molecule) in the cytoplasm. Further breakdown of pyruvate occurs in different ways in different organisms, as shown below:
3. How is oxygen and carbon dioxide transported in human beings?
Answer:
- Oxygen Transport: Haemoglobin present in the blood takes up oxygen from the air in the lungs and carries it to all tissues.
- Carbon Dioxide Transport: CO2 is more soluble in water. Therefore, it is mostly transported from tissues in the dissolved form in blood plasma to the lungs, where it diffuses from blood to air.
4. How are the lungs designed in human beings to maximise the area for exchange of gases?
Answer:
In the lungs, the air passage divides into smaller branches called bronchi, which further divide into fine branches called bronchioles. The bronchioles terminate in balloon-like, thin-walled structures called alveoli. The alveoli provide maximum surface area for gas exchange.
Page 110
1. What are the components of the transport system in human beings? What are the functions of these components?
Answer:
Heart, blood, and blood vessels.
- Function of heart: It receives deoxygenated blood from the body parts and pumps it to the lungs for oxygenation. It receives purified blood from the lungs and pumps it to various body parts.
- Function of blood: It transports oxygen, CO2, nutrients, hormones, and nitrogenous wastes. It also protects the body from diseases and regulates body temperature.
- Function of blood vessels: They carry blood from the heart to body parts and vice versa.
2. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Answer:
Mammals and birds need a constant supply of oxygen to get energy to maintain their body temperature. Separation of oxygenated and deoxygenated blood allows sufficient supply of oxygen to the body.
3. What are the components of the transport system in highly organised plants?
Answer:
There are two conducting tissues called xylem and phloem.
- Xylem: Consists of vessels, tracheids, and other xylem tissues. The interconnected vessels and tracheids form a continuous system of water-conducting channels reaching all parts of the plant. Xylem carries water and minerals.
- Phloem: Conducts products of photosynthesis from leaves to different plant parts.
4. How are water and minerals transported in plants?
Answer:
In xylem tissue, vessels and tracheids of the roots, stems, and leaves are interconnected to form water-conducting channels reaching all parts. At the roots, cells actively take up ions from the soil, creating a difference in the concentration of ions between the root and soil, so water moves into the root from the soil. Thus, there is a steady movement of water into the root xylem. Water is lost from the leaves as vapor through stomata, called transpiration. This loss is replaced by water from the xylem vessels in the leaf. Transpiration creates a suction that pulls water from the xylem cells of roots, helping in the absorption and upward movement of water and minerals from roots to the leaves.
5. How is food transported in plants?
Answer:
Transport of soluble products of photosynthesis (food) from leaves to other parts through phloem is called translocation. It needs energy. These substances are delivered to the storage organs of roots, fruits, and seeds and to growing organs. Translocation takes place in the sieve tubes with the help of adjacent companion cells in both upward and downward directions. Material like sucrose is transferred into phloem using energy from ATP. This increases the osmotic pressure of the tissue, causing water to move into it. This pressure moves the material in the phloem to tissues.
Page 112
1. Describe the structure and functions of nephrons.
Answer:
Each kidney has a large number of filtration units called nephrons.
Structure: At the end of each nephron, a cup-shaped structure called Bowman’s capsule encloses a cluster of very thin-walled blood capillaries called the glomerulus. There is a long and coiled tubular part in the nephron starting from the Bowman’s capsule.
Function: In the glomerulus, blood is filtered, and the Bowman’s capsule collects the filtrate. Glucose, amino acids, salts, and a major amount of water in the initial filtrate are selectively reabsorbed in the tubular part. The remaining filtrate is excreted as urine.
2. What are the methods used by plants to get rid of excretory products?
Answer:
- Gaseous products are removed through stomata in leaves and lenticels in stems.
- Solid and liquid wastes are removed by shedding off leaves, peeling off bark, and felling off fruits.
- Secretion of wastes in the form of gums and resins.
3. How is the amount of urine produced regulated?
Answer:
The amount of urine is regulated by the kidney based on the amount of excess water in the body and the amount of dissolved waste to be excreted. When water is in excess, large quantities of dilute urine are excreted. When water is less, a small quantity of concentrated urine is excreted. When there are more dissolved wastes in the body, more water is required to excrete them, so the amount of urine produced increases.