InstructorPriyanka Pandey
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Indian Institute of Technology Bombay

Life Processes


The concepts that are going to be discussed in this course are:

  1. Nutrition
    1. In autotrophs
    2. In amoeba
    3. In humans
  2. Respiration
    1. Aerobic and anaerobic
    2. In humans
  3. Transportation
    1. In humans
    2. In plants
  4. Excretion
    1. In Humans
    2. In plants

Nutrition in autotrophs:

Autotrophs fulfil their food and energy requirements by the process of photosynthesis. The steps that take place during photosynthesis are:

(i) Absorption of light energy by chlorophyll.

(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.

(iii) Reduction of carbon dioxide to carbohydrates.

The carbon dioxide required by the plant is obtained through tiny pores present on the surface of the leaves called stomata. Note that the exchange of gases occurs across the surface of stems, roots and leaves as well. Water used in photosynthesis is taken up from the soil by the roots in terrestrial plants. Other materials like nitrogen, phosphorus, iron and magnesium are taken up from the soil.

Important diagrams – from this unit, diagramatic representation of cross-section of a leaf and stomatal pores can be asked, so make sure you practice drawing them atleast once before the exam.

Cross-section of the leaf:

Open and closed Stomatal Pore:

Nutrition of Amoeba:

Amoeba takes in food using temporary finger-like extensions on the cell surface which fuse over the food particle forming a food-vacuole. Inside the food vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm.

Important diagram – amoeba engulfing a food vacuole

Nutrition in Humans:

The human digestive system is responsible for processing the food that we eat, and providing us with energy.

  1. The process starts in our mouth, where our teeth help in crushing the food. Saliva makes the food wet, for easy movement through the alimentary canal.
  2. From mouth, the food is taken to stomach via the oesophagus. Gastric glands present in the walls of the stomach release HCl, pepsin and mucus.
  3. From stomach, the food is released into the small intestine, where digestion of carbohydrates, fats and proteins takes place. This is done with help from secretion of liver and pancreas.
  4. The digested food is taken up by the walls of the intestine, which contains numerous finger-like projections called villi.
  5. The unabsorbed food is sent into the large intestine where more villi absorb water from this material.
  6. The rest of the material is removed from the body via the anus.

Here, note that there are some enzymes involved in the process, which help in the process of digestion. The names and functions of these enzymes can be asked in exam for 1 mark, so we suggest that you read this section from NCERT thoroughly.

Check this diagram of Human Alimentary Canal, which can be asked in exam, so do practice it.

Aerobic and Anaerobic Respiration

Respiration refers to the process by which nutrients in the cell are converted into useful energy. If this process takes place in the absence of air (oxygen), it is called anaerobic respiration. In the presence of oxygen, it is referred to as aerobic respiration. It can also sometimes take place in lack of oxygen, as depicted in the following chart:

Note the different products formed in each case, as they can be asked in exam.

The energy released during cellular respiration is used to synthesize a molecule called ATP which is used to fuel all other activities in the cell.

Respiration in humans:

Let us now see how respiration takes place in humans. We have broken down the process in points for better understanding, which you can now see on your screen.

  1. In human beings, air is taken into the body through the nostrils and is filtered by fine hair that line the passage.
  2. The air passes through the throat where rings of cartilage are present, which ensure that the air-passage does not collapse.
  3. The air then reaches the lungs, where the passage divides into smaller and smaller tubes which finally terminate in alveoli.  These alveoli are the places where exchange of gases takes place.
  4. The blood brings carbon dioxide from the rest of the body, which is released into the alveoli, and the oxygen in the alveolar air is taken up by blood, to be transported to all the cells in the body.
  5. Now the oxygen that is taken in our body, has to be transported all parts of the body. This is done by the respiratory pigment called haemoglobin, present in red blood cells.

Transportation in Human Beings:

Most of the nutrients, waste products, useful gases, etc are carried by our blood. Thus, this blood needs to be pushed to each and every corner of the body, that too continuously! This job of pumping the blood around the body is done by our heart!

The heart is a muscular organ which is as big as our fist.

Now, since both oxygen and carbon dioxide have to be transported by the blood, the heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide.

Now let us see how this happens!

On your screen you now see sectional view of the human heart, which you should definitely practice drawing as it has been asked in previous years.

  1. The oxygen-rich blood from the lungs comes to the upper-left chamber of the heart, the left atrium. The left atrium relaxes when it is collecting this blood and then contracts, while the next chamber, the left ventricle, expands, so that the blood is transferred to it. When the muscular left ventricle contracts in its turn, the blood is pumped out to the body.
  2. De-oxygenated blood comes from the body to the upper – right chamber, the right atrium, as it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates. This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation.

Note that not all organisms have 4-chambered heart. Amphibians or many reptiles have three-chambered hearts, while fishes, on the other hand, have only two chambered hearts.

This pumping of heart around the body takes place through blood vessels called veins and arteries. On your board now you can see differences in these two, and you should remember them.

Arteries Veins
Vessels which carry blood away from the heart to various organs of the body collect the blood from different organs and bring it back to the heart
These have thick, elastic walls as blood emerges from heart under high pressure. They have valves that ensure blood flows in only one direction
These are  usually positioned deeper within the body These are present closer beneath the surface of the skin

Two major components of blood are platelets and lymph. You can read more about these on your screen now.

  1. Platelets – when we are injured, blood starts flowing out of the body. This can cause a decrease in blood pressure, decreasing efficiency of pumping system. Platelet cells circulate around the body and plug such leaks by helping to clot the blood at these points of injury.
  2. Lymph – When some amount of plasma, proteins and blood cells leak through the capillaries, they form lymph. It is colourless and contains less protein. It carries digested and absorbed fat from intestine and drains excess fluid from extra-cellular space back into the blood.

Transportation in Plants:

In plants, most of the nutrients are taken up from the soil, and transported to plant parts by diffusion. If the plant, however, is large, diffusion is not sufficient and proper transporting system is required. This is achieved by xylem and phloem.

  1. Xylem moves water and minerals obtained from the soil.
  2. Phloem transports products of photosynthesis from the leaves where they are synthesised to other parts of the plant.

How exactly they achieve this transportation, let us see now.

  1. In xylem tissue, vessels and tracheids form a continuous system or a channel which reaches all parts of the plant. At the roots, cells in contact with the soil take up ions. Due to this concentration gradient of ions between roots and soil, water moves from the soil to the roots. Also, transpiration of water from leaf cells creates a suction, which pulls up water to upper parts of the plant.
  2. The transport of food and other substances takes place both in upward and downward directions. This transport is achieved by utilising energy from ATP.

Excretion in Humans:

The biological process involved in the removal of various harmful metabolic wastes from the body is called excretion.
The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
Let us see this process in detail now.

  1. The basic filtration unit in the kidneys, is a cluster of blood capillaries.
  2. Each such cluster is associated with the cup-shaped end of a tube, that collects the filtered urine. These filtration units are called nephrons, and each kidney contains several such clusters.
  3. The urine forming in each kidney then enters the ureter, which connects the kidneys with the urinary bladder.
  4. Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.

From this topic, there are two important diagrams, which you can now see on your screen.

Excretory system in human beings:

Nephron:

 

Excretion in Plants:

Different waste substances are excreted by plants in different ways:

  1. Waste gases are given out through stomata
  2. Excess water is removed by transpiration
  3. Many waste products are stored in leaves, which eventually fall off
  4. Some waste substances are excreted off in soil
Section 1Process of Photosynthesis
Section 2Process of Digestion
Section 3Process of Respiration
Section 4Transportation in Animals
Section 5Transportation in Plants
Section 6Process of Excretion