Life Processes Class 10 Notes

 Life Processes

 

 Introduction 

Before we learn about the various life process, we should know the defining characteristics of life. How do we understand what is alive and what is not? We see a variety of things such as mountains, lands, buildings, plants, etc. around us. How do we differentiate these things? Some of these are living, and some of these are nonliving things.  All living things carry out various life processes like taking in food, obtaining energy from food, throwing out wastes, and so on. Living things also grow, move, respond to change in their external and internal conditions, and produce young ones. 

All living things (organisms) also have an organized (cellular) structure with different levels of the organization.  An organized structure with cells, tissues, organs, organ systems, etc., is an important feature that distinguishes the living from the nonliving. 

The characteristics of living things

i) Living things can move by themselves. 

ii) Living things can grow.

iii) Living things can respond to changes around them.

iv) They can respire.

v) Living things can reproduce.

vi) They can respire.

Life Processes 

The basic functions performed by living organisms to maintain their life on this earth are called life processes. Nutrition, respiration, transportation, excretion, control & coordination, growth, movement and reproduction. 

Nutrition 

Different life processes of an organism, like growth and maintenance, require energy which is obtained from food by the process called nutrition. 

Or 

The Process of intake and utilisation of food by an organism is called nutrition. 

Modes of Nutrition

Modes of nutrition mean methods of procuring food or obtaining by an organism. 

i) Autotropic
ii) Heterotrophic 

Plants and animals do not obtain food by the same process. Plants and some bacteria have the green pigment chlorophyll to help synthesize food, while animals, fungi, and other bacteria depend on the other organism for food. Based on this, there are two main modes of nutrition: autotrophic and heterotrophic. 

Autotrophic nutrition

The term 'autotroph' is derived from two Greek words autos (self) and trophe (nutrition). In autotrophic nutrition, an organism makes its own food from simple raw materials. 

Mode of nutrition in which an organism makes  (or synthesizes) its own food from the simple materials like `CO_2, H_2O` present in the surroundings, with the help of sunlight.  

Nutrition in green plants

Photosynthesis

Photosynthesis is a process by which green plants, having chlorophyll, synthesize the simple sugar (glucose) from the simple raw materials water and carbon dioxide using the energy of sunlight. Oxygen is released in this process. 

`6CO_2 + 12H_2O  \overset {sunlight}{\rightarrow} C_6H_12O_6 + 6H_2O + 6O_2`

The sugar produced is stored in the form of starch. Since autotrophic plants are able to produce food, they are also known as producers.  

Site of photosynthesis 

Though all green parts of the plant are capable of performing photosynthesis, the leaves are the most suitable organs for this process. The cells of the leaves contain special organelles called chloroplast, which are the main sites of photosynthesis. 

Requirements for photosynthesis 

1. Chlorophyll 
2. Carbon dioxide
3. Water
4. Sunlight 

1) Chlorophylls are the green pigments found in all photosynthetic organisms and are responsible for their green colour. In plants, chlorophyll is mainly found in the leaves. Young stems and fruits may also have chlorophyll. In plant-like 'algae', the whole plant is green and takes part in photosynthesis.  

2)  Air contains about 0.04% of carbon dioxide. Terrestrial plants use atmospheric carbon dioxide in photosynthesis. Aquatic plants use the `CO_2` dissolved in water. Plants obtain `CO_2` through pores called stomata  present on the surface of leaves. The opening and closing of these pores are regulated by guard cells, which surrounded them. 

Open and closed stomatal pore

3) Water is an important raw material for photosynthesis. Plants absorb water from the soil through their roots hair. The water is then transported up to the leaves through the stem.

4) The energy of sunlight is used in splitting water molecules into hydrogen and oxygen. The splitting of water in the presence of light is called photolysis.  

Mechanism of Photosynthesis

• Light energy is first absorbed by the chlorophyll molecules found inside the chloroplasts. 
• The absorbed energy causes the splitting of water molecules into hydrogen and oxygen. The splitting of water in the presence of light is called photolysis. During this process, light energy is converted into chemical energy. 
• Finally, carbon dioxide is reduced to carbohydrates (the end product of photosynthesis).

Factors affecting photosynthesis

1. External factors 

• Intensity of light
• The concentration of `CO_2` in the atmosphere
• Temperature
• Water

2. Internal factors 

• Chlorophyll
• Accumulation of the products of photosynthesis. 

Experiments

1.  Experiments to demonstrate that starch is formed during photosynthesis. 

Pluck a healthy green leaf of a plant that was in the sunlight. Boil it in the water for about 2 minutes. Now transfer the leaf to a beaker containing alcohol. You will observe that the leaf turns white, indicating that chlorophyll has been removed. Place the leaf in a dilute solution of iodine. This turns the leaf into bluish-black, this shows that the leaf contains startch.  

2. Experiment to demonstrate that carbon dioxide is essential for photosynthesis. 

Get two healthy potted plants of almost the same size and place them in the dark for 24 hours. Cover the plants with separate bell jars. Keep some crystals of potassium hydroxide (`KOH`) in a petri dish and place them under one of the jars. Keep the plants in sunlight for photosynthesis to take place. After 3 to 4 hours pluck a leaf from each plant. Remove the chlorophyll. Now use a few drops of iodine to test for starch in each leaf. Only one leaf turns blue-black, showing the presence of starch. This happens because `KOH` absorbs `CO_2` present inside one bell jar. The leaves do not get `CO_2` for photosynthesis. 

`CO_2` is essential for photosynthesis

3. Experiment to show that sunlight is essential for photosynthesis. 

Keep a potted plant in the darkroom for 24 hours. On one of the leaves, stick a black paper strip. Now, place this plant in sunlight for few hours. Pluck the leaf and remove the black strip. Also, remove the chlorophyll. Add few drops of iodine solution. The leaf turn blue-black except in the region that had been covered. This region did not receive light and hence no starch was formed. The uncovered region received light and starch was formed due to photosynthesis.  

Sunlight is essential for photosynthesis

Heterotrophic Nutrition

The word 'heterotroph' is derived from two Greek words - 'heteros' (others), and 'trophe' (nutrition).  Heterotrophic organism obtains their food from other organisms. Each organism is adapted to its environment.

There is a range of strategies by which the food is taken in and used by the organism.

 ➤ Some organisms break down the food material outside the body and then absorb it. Examples are fungi like bread moulds, yeast, and mushrooms.

Bread moulds 

Image Source: https://en.wikipedia.org/wiki/Rhizopus_stolonifer

➤ Others take in whole material and break it down inside their bodies. What can be taken in and broken down depends on the body design and functioning.

➤ Some other organisms (Parasites) derive nutrition from plants or animals without killing them. This parasitic nutritive strategy is used by a wide variety of organisms like Cuscuta, ticks, lice, leeches, and tapeworms.

Cuscuta

Image Source: https://en.wikipedia.org/wiki/Cuscuta 

How do Organisms obtain their Nutrition?

The food and the way it is obtained differ, the digestive system is different in various organisms.

➤ In single-celled organisms, the food may be taken in by the entire surface. For example, Amoeba (fig. a)  takes in food using temporary finger-like extensions (Pseudopodia) of 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. The remaining undigested material is moved to the surface of the cell and thrown out. In Paramecium (fig. b), which is also a unicellular organism, the cell has a definite shape, and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell.

Amoeba and Paramecium 

NUTRITION IN HUMAN BEINGS

Nutrition in human beings takes place through the human digestive system. The human digestive system consists of the alimentary canal and its associated glands. 

Human digestive system  `=`  Alimentary canal `+`   Associated glands. 

The canal can be divided into various compartments: 

(1)  buccal cavity

(2) food pipe or oesophagus, 

(3) stomach, 

(4) small intestine, 

(5) large intestine ending in the rectum  

(6)  anus. 

The glands which are associated with the human digestive system are:

(1) salivary glands

(2) liver

(3) pancreas 

The various steps of nutrition in human beings are:

(1) ingestion

(2) digestion

(3) absorption

(4) assimilation

(5) egestion 

(1) Ingestion

Human beings have a special organ for the ingestion of food, it is called the mouth. 

(2) Digestion

The digestion of food begins in the mouth. The mouth cavity (buccal cavity) contains teeth, tongue and salivary gland.  The teeth cut the food into small pieces. So, the teeth help in physical digestion. The salivary gland in our mouth produces saliva, a watery liquid, it wets the food. The wetted food can be swallowed more easily. The salivary gland help in chemical digestion by secreting enzyme (salivary amylase) which digest the starch present in food into sugar. 

Respiration 

The process of releasing energy from food is called respiration.

The process of respiration involves taking oxygen into the cells and using it for releasing energy by burning food and then eliminating the waste products `CO_2` and `H_2O` from the body. 

Food + Oxygen `rightarrow` Carbon dioxide + Water + Energy

The process takes place inside the cell, so it is also known as cellular respiration. 

Work in progress. 






References

1. Foundation Science Biology Class 10
2. NCERT Science Class 10
3. Wikipedia