Life Processes (a) Nutrition

In photosynthesis, sunlight is used along with water, CO₂ and chlorophyll to prepare food. The mode of nutrition here is autotrophic. Example of autotrophic organisms is green plants that make their own food and do not depend on any organism for their nutrition.

The process of photosynthesis occurs in green parts of a plant, basically leaves. The presence of chlorophyll (green pigment) is necessary for photosynthesis to occur and chlorophyll is present in leaves as green dots.

The process of the photosynthetic process is depicted here:

The chloroplast acts as the site of photosynthesis. It is a cell organelle that is covered by a double membrane and it contains chlorophyll. It is present in green tissues of plants, especially leaves. Chloroplasts absorb sunlight to conduct photosynthesis.

The raw materials needed to carry out photosynthesis are water (absorbed through roots), CO₂(diffused in from the air through stomata). In addition to these, chlorophyll (green pigment present in chloroplasts) and sunlight are also required. Without these materials, photosynthesis cannot occur.

Fungi are heterotrophic organisms. They depend on other organisms to obtain nutrition. They show the saprobic mode of nutrition or saprotrophic nutrition. They break down the food material outside their body by secreting digestive enzymes and absorb nutrition from it.

Parasitic organisms like tapeworms, leeches, orchids, etc obtain nutrition from other living organisms (plants or animals) called as host, without killing them. Parasites may live on the outside or inside the body of its host. They cause harm to the body of the host.

Ingestion refers to the consumption of food, water and other substances through the mouth into the gut. Ingestion is a general term used for taking in any substance into the digestive system.

Pseudopodia (singular: pseudopodium) are temporary finger-like elongated protrusions of cell surface of unicellular organisms (Amoeba) used for feeding and locomotion. They are formed by cytoplasmic streaming (streaming movement of cytoplasm). It is also called as false foot.

There are 3 major salivary glands.

Parotid gland - largest salivary gland located in front of the ears, one on each side.

Sublingual gland – smallest salivary gland located beneath the tongue.

Submandibular gland – located beneath the floor of the mouth.

Carnivores have shorter small intestine, as compared to herbivores. Carnivores consume only flesh of other animals whereas herbivores consume plant products, which contain cellulose and fibre. Meat is relatively easier to digest and provide more energy. Cellulose and other plant products take longer to be digested. Hence, carnivores possess shorter small intestine.

Villi are small finger-like projections present in the inner lining of the small intestine. They increase the surface area of small intestine by providing more area for efficient absorption of nutrients. The presence of villi and micro-villi gives a brush border appearance. Villi also possess blood vessels and lacteals (lymphatic vessels).

Bile juice (dark green-yellow pigment) is produced by the liver. It helps in the digestion of lipids (fats) in small intestine. It emulsifies (breaks down) larger fat globules into smaller ones so that enzymes can act efficiently on fat globules.

The food that we eat must pass along the digestive system in a regulated manner so that it is processed properly. Peristalsis refers to the involuntary rhythmic wave-like contractions and relaxations of the smooth muscles of alimentary canal. This process is responsible to push the food forward along the gut. It aids in the smooth movement of food through different digestive organs.

Water and carbon-dioxide are the two raw materials responsible for the release of oxygen during photosynthesis. Water is absorbed from soil through the roots and CO₂ diffuses from the air into the plant through stomata. These raw materials are then converted into energy-yielding glucose molecules.

In an animal body, extra glucose or carbohydrate is stored in the liver as well as in skeletal muscles in the form of glycogen. Glucose is converted to glycogen (starch-like carbohydrate) in liver. When the body is in need of energy, glycogen is converted back into glucose.

Glycogen is an energy rich carbohydrate that is stored in large quantities in the liver and skeletal muscles of the body. It is a branched-chain polymer of glucose. It serves as a reserve source of energy.

The digestion of proteins occurs in the stomach. It is facilitated by digestive enzymes (pepsin, hydrochloric acid). HCl provides acidic medium while pepsin acts on proteins and breaks them into smaller peptides.

Most CO₂ reach the photosynthesising cells of green leaves through diffusion. Stomata (tiny pores) present of leaf surface and stem facilitates gaseous exchange between the plant cells and the surrounding. CO₂ move into the cells through these small pores.

The digestion of starch (complex carbohydrate) produces glucose and maltose (simple sugars).

Fats are broken down to produce molecules of glycerol and fatty acids.

If the liver of a person get damaged, fat digestion would be affected. As a result, liver will not produce bile efficiently and the emulsification of fats will stop.

The rate of photosynthesis increases with the increase in temperature, only upto a certain limit. For every 10⁰ rise, the rate is almost doubled. The plants show maximum photosynthesis at optimum temperature. It is between 20-30^o C. Further increase in temperature leads to decrease in the rate of photosynthesis as the enzymes get denatured at high temperature and do not work efficiently.

Desert plants close their stomata during the day to prevent transpiration and loss of water. To perform photosynthesis, CO₂ is necessary. They take up CO₂ during the night through stomata and store it in their photosynthesising cells in the form of an intermediate until the day. And when sunlight is available, they perform photosynthesis to make their food. This is called as CAM (Crassulacean acid metabolism) photosynthesis.

(i) This reaction represents the process of photosynthesis.

During photosynthesis, 1 molecule of glucose (carbohydrate) and 6 molecules of oxygen are produced using the raw materials water (6 molecules) and carbon dioxide (6 molecules) in the presence of chlorophyll and light energy. Here, reduction of CO₂ occurs.

(ii) The presence of chlorophyll is necessary for photosynthesis to occur. Its most important function is to absorb energy from incoming light and transfer this absorbed energy to the reaction centres (part of photo-system)

The leaves containing the green pigment chlorophyll (present in chloroplast) helps the plant to perform photosynthesis by trapping light energy. The plant absorbs CO₂ through stomata and reduces it to glucose. The presence of chloroplasts and stomata helps the plants to make food.

The process of photosynthesis involves a few events that may not occur immediately after one another. There might be a time lag between them.

•The chlorophyll present in chloroplasts absorbs energy from sunlight.

•This light energy is then converted into chemical energy which is used for making food.

•The water molecules split to give hydrogen and oxygen.

•Finally, CO₂ absorbed is reduced to form glucose (carbohydrate).

Plants and animals have a completely different mode of nutrition. Plants are autotrophic organisms that are capable of making their own food by performing photosynthesis using 2 raw materials (water + CO₂).

They need light energy to make their own food. Plants do not depend on any organism to obtain nutrition. On the other hand, animals are heterotrophic organisms that depend on other organisms (plants and other animals) to fulfill their nutrition requirements. They cannot make their own food.

Stomata are tiny pores present on the surface of leaves and stems of plants. It performs the following function:

•It facilitates the exchange of gases between plant and its surroundings. It is through stomata that plant release oxygen and take up carbon dioxide.

•It helps the plant to get rid of excess water through transpiration. The stomata also close down to prevent loss of water. Thus, it regulates the water content in plant cells.

The figure for stomata is given below:

The raw materials needed to carry out photosynthesis are water (absorbed through roots), CO₂(diffused in from the air through stomata).

In addition to these, chlorophyll (green pigment present in chloroplasts) and sunlight are also required to make food. Without these materials, photosynthesis cannot occur. The reaction involved is given below.

i. Chapati is a complex carbohydrate. The digestion of carbohydrates begins in the mouth.

ii. The starch present is acted upon by salivary amylase (secreted by salivary glands) and is broken down to simpler sugars (e.g. maltose).

iii. It is then passed along the gut by peristaltic movements. It then reaches the stomach and gets mixed up with the gastric juices. But no digestion of carbohydrates occurs in stomach.

iv. The food is then passed into the small intestine, where major digestion of carbohydrates takes place.

v. The intestine receives enzymes from pancreas and liver. The pancreatic amylase further breaks downs the sugars into glucose to be absorbed easily. Thus, the digestion of chapati is completed.

vi. The diagram is given below:

(i) Yes, plants depend on solar energy to produce food. They require energy from sunlight to perform photosynthesis. If sunlight is not available, they will not be able to make their own food.

(ii) We (humans) are heterotrophic organisms. We obtain nutrition from plant and animal resources. We use plant products as food. All organisms require nutrition, but they use different strategies. Some organisms consume food by breaking down it into smaller parts. Unicellular organisms like Amoeba use pseudopodia to gather food.

(iii) Removal of green cover (deforestation) leads to serious problems. It has a negative impact on our environment and our lives. As we are directly dependent on plants and trees for our food, our survival will be at risk. Deforestation leads to climatic changes. It is a major cause for global warming. Moreover, animals are also badly affected. Their habitats are destroyed.

(i) Raw green plants contain fibre and cellulose. Our digestive system does not secrete any enzyme capable of digesting cellulose. Cellulose is digested by enzyme cellulose present in ruminating animals like cow. Also, our oesophagus serves only as a pathway to transport food from mouth to stomach. It does not possess any digestive gland. Hence, no secretion of enzymes occurs.

(ii) Although we may require enzyme action any time, they must be produced in an inactive form. Enzymes are capable of digesting a variety of bio molecules (proteins, fats, etc). If produced in active form, they may act upon the body cells and tissues and digest them leading to degeneration of body tissues.

(iii) Although HCl provides a highly acidic medium in our stomach, but it does not harm the walls of the stomach. The mucus-secreting cells (goblet cells) present in the inner lining of stomach secretes mucus and lines the wall of stomach with a mucus layer. Thus, prevents it from the action of HCl.

(iv) The student has a thirst for knowledge. He is curious to know about the human body and what happens to the food that we eat.

In photosynthesis, water and carbon dioxide are used as raw materials to produce glucose and release out oxygen. This process occurs in the presence of green pigment chlorophyll present in leaves of the plant, which remains unchanged after the reaction.

Chloroplasts are usually present in mesophyll cells of leaves placed near the upper epidermis. Guard cells surrounding the stomata also possess chloroplasts.

Most plants absorb nitrogen in the form of nitrates, nitrites and urea. They cannot use up atmospheric nitrogen as it is un-reactive. This nitrogen needs to be converted into absorbable forms by certain nitrogen-fixing bacteria so that they can be taken up by plants.

For photosynthesis to occur, both sunlight and CO₂ are required. The plant forms glucose (later on converted to starch) through photosynthesis. The part Q of leaf was covered and not exposed to light and part R was kept in absence of CO₂. Thus, both parts of leaf did not form starch and gave a negative test for starch. (Note - iodine solution gives a positive test for starch and turns blue-black in colour)

The presence of villi and microvillus in the inner lining of small intestine increases the surface area for absorption. They allow more area for the enzymes to work efficiently.

Egg white contains only protein, and no fat. The digestion of proteins occurs in stomach and proteins are converted into amino acids. So amino acids will be found leaving the stomach. The absorption of amino acids occurs in small intestine. So, only water will be found leaving the small intestine.

•Ingestion – consumption/taking in of food

•Digestion – breaking up of food particles into small fragments

•Absorption – absorption of broken down food particles into the blood

•Assimilation – soluble food molecules move to different organs to provide energy through blood

Digestive enzymes are secreted by salivary glands (salivary amylase), stomach (pepsin), pancreas (amylase, lipase) and small intestine (trypsin). Liver produces bile juice and it only emulsifies (breaks down) fats and does not digest them.

Chewing increases the surface area of food. Large food particles are broken down into small fragments. Salivary amylase secreted by salivary glands acts on carbohydrates (starch) present in food and converts it into maltose. Saliva does not act on fats.