The process of photosynthesis is affected by two types of factors namely:

1. Internal factors
   1. Chlorophyll
   2. Leaf anatomy
   3. Accumulation of end products and
   4. Hormones
2. External factors
   1. Carbon dioxide
   2. Water
   3. Sunlight
   4. Oxygen and
   5. Temperature

Internal factors

1. Chlorophyll
The process of photosynthesis depends on the amount of chlorophyll present in the leaf. If chlorophyll is absent in a leaf, photosynthesis does not takes place.

2. Leaf anatomy
Leaf anatomy also influences the photosynthesis. The important anatomic structures which influence photosynthesis are size, shape, position and frequency of stomata.

3. Accumulation of end products
If the end products of photosynthesis are translocated at a slow rate, the rate of photosynthesis reduces.

4. Hormones
The rate of photosynthesis is also influenced by certain hormones present in a plant such as cytokinins, gibberellins and abscisic acid. Cytokinins and gibberellins increase the rate of photosynthesis, while the abscisic acid reduces it.

External factors

1.Carbon dioxide 
The amount of carbon dioxide in the atmosphere is 0.03%. If the amount of CO₂ increases up to 0.1%, the rate of photosynthesis also increases. But, the rate of photosynthesis decreases, if the amount of CO₂ increases beyond 0.1%.

2. Water
Water is a very important raw material for photosynthesis. A slight decrease in amount of water causes closing of stomata. This results in less absorption of CO₂ in leaves, hence the process of also slows down..

3. Sunlight
Photosynthesis does not take place in dark. If the intensity of sunlight is increased slowly, the rate of photosynthesis increases up to a certain point (called saturation point). If the intensity of sunlight increases beyond saturation point, then photosynthesis slows down.

4. Oxygen
It is observed that a small quantity of oxygen is essential for photosynthesis, whereas a high quantity of oxygen slow down the rate of photosynthesis.

5. Temperature
At low temperature the rate of photosynthesis is slow. As the temperature is increased, the rate of photosynthesis also increases up to a certain point. But a high increase in temperature slows down the rate of photosynthesis.

Test Your Understanding and Answer These Questions:

1. Explain the various factors which affect the rate of photosynthesis?

Facts about Hydrogen

The name Hydrogen is derived from the Greek words ‘Hydro’ and ‘Genes’ which together mean ‘Water Forming’ because water molecules contains atoms of hydrogen. It is the lightest element known. It is the most abundant element in the universe. Almost all stars and planets in this universe consist of hydrogen. In nature hydrogen is mainly found in the form of water and hydrogen gas. Pure hydrogen gas can be prepared in the lab by electrolysis of water.

Hydrogen (Protium) is the only element in periodic table having 0 neutrons in its nucleus.

Every living organism requires food to fulfill the requirement of energy for their various activities. Green plants are autotrophic in nature. So, they synthesize their food by a very important process called photosynthesis. The term ‘photosynthesis’ consists of two words ‘photo’ means ‘light’and ‘synthesis’ means ‘to make’. Thus, photosynthesis is the process of making food with the help of sunlight.

It may be defined as the process of making food by green plants from carbon dioxide and water by chlorophyll in the presence of sunlight. In the process of photosynthesis oxygen gas is liberated. The chemical reaction for photosynthesis is as follows:

The process of photosynthesis takes place in leaves of a plant, because these contain the green colouring pigment chlorophyll which is necessary for synthesis of food in plants. Thus, leaves are the site of preparation of food in plants. That is why; leaves are also called food factories of a plant.

The carbon dioxide required for photosynthesis is obtained from the air which enters the leaves through very minute pores called stomata. But, aquatic plants use carbon dioxide dissolved in water. The water is absorbed from the soil by the roots of plants and transported to leaves by a network of tiny veins called xylem vessels. The sunlight energy is absorbed by chlorophyll. A chemical reaction using the trapped sunlight energy takes place in the chloroplasts (chlorophyll containing organelles of cells) to prepare food. The food prepared by the leaves of a plant is usually in the form of carbohydrates.

Significances of photosynthesis

1. Food is prepared by photosynthesis which is used by all the plants and animals
2. Photosynthesis decreases the amount of CO₂ present in atmosphere; hence it helps in reducing pollution.
3. During the process of photosynthesis O₂ gas is produced as a byproduct, which is used for respiration by animals.
4. During photosynthesis CO₂ is used by plants and O₂ is liberated. So, photosynthesis helps in maintaining the balance between CO₂ and O₂ present in air.
5. Many photosynthetic products such as coal, petroleum and natural gas are important sources of energy which are used to run our machines.

Test Your Understanding and Answer These Questions:

1. What is photosynthesis?
2. How do plants obtain food?
3. Which is main product of photosynthesis?
4. Which is by product of photosynthesis?
5. What is importance of photosynthesis?
6. Write the names of raw materials of photosynthesis.
7. From where do plants get CO2 for photosynthesis?
8. From where do aquatic plants get CO2 for photosynthesis?

In this type of nutrition, the organisms (called parasites) depend on the body of other living organisms (called their host) for getting their food. Many viruses, bacteria, fungi and animals have this mode of nutrition.

The organisms which depend on other living organisms (host) for food are called as parasites.

Parasites of two types:

• a) Ecto parasites
• b) Endo parasites

Ecto parasites

Ecto parasites are those parasites which obtain their food from their host by remaining outside the body of their host. For example, mosquitoes, ticks, lice and bed bug.

Endo parasites

Endo parasites are those parasites which obtain their food from their host by remaining inside the body of their host. For example, Ascaris, plasmodium vivax and tape worm.

Test Your Understanding and Answer These Questions:

1. Define parasites.
2. Explain types of parasites by giving two examples in each case.
3. Write names of two ectoparasites.
4. Write names of two endoparasites.

In saprophytic nutrition the organisms obtain their food from dead and decaying organic matter of dead plants, dead animals and other decomposing organic matter. And the organisms which obtain their food from dead and decaying organic matter of dead plants, dead animals and other organic matter are called saprophytes. Fungi, bread mould, some protists and many bacteria are saprophytic in nutrition.

In this type, the saprophytic organisms like fungi release digestive enzymes in their surrounding medium to convert the complex organic molecules such as sugars in simple forms such as glucose. This simple food is then absorbed through the body surface, and utilized for various activities by fungus.

Test Your Understanding and Answer These Questions:

1. What do you meant by saprophytic nutrition?
2. Define saprophytes. Give examples of saprophytes.
3. Explain nutrition in fungi.

The organisms having holozoic nutrition are further classified in three categories. These are:

1. Carnivores
2. Herbivores and
3. Omnivore  

Carnivores

The organisms which eat other animals or meat only are called carnivores. For example, lion, bear, snake, crocodile, lizard, eagle and wolf etc.

Herbivores

The organisms which consume or eat only plants as their source of food are called herbivores. For example, cow, rabbit, goat, deer, locust and camel etc.

Omnivores

The organisms which eat both plant food as well as meat of animals are called omnivores. The best examples of omnivores are human beings, crow, dog, sparrow and ants etc.

Test Your Understanding and Answer These Questions:

1. Explain different types of organisms based on their modes of nutrition.
2. Define herbivores. Give examples of herbivores.
3. Define carnivores. Give examples of carnivores.
4. What are omnivores. Give examples of omnivores.
5. Write differences between herbivores and carnivores.
   n.

A heterotrophic organism can obtain its food from other organisms in following three ways:

1. Holozoic nutrition
2. Saprophytic nutrition
3. Parasitic nutrition

Holozoic nutrition

Holozoic nutrition takes place in those organisms which take solid or liquid food through the mouth inside their body Examples of organisms having holozoic mode of nutrition are human beings, dog, cat, lion, deer, crow, frog and fish etc. This process takes place in following steps:

1. Ingestion
The process of taking food inside the body is called ingestion.

2. Digestion
In digestion the ingested food is converted into simple form with the help of digestive enzymes.

3. Absorption
In this stage the food digested in second step is absorbed into the cells of body.

4. Assimilation
Assimilation is the process of utilizing the food absorbed in third step by various cells of the body.

5. Egestion
Egestion is the final step of holozoic nutrition in which the undigested food is removed from the body.

Test Your Understanding and Answer These Questions:

1. Define ingestion.
2. What is assimilation?
3. Define digestion.
4. What is holozoic nutrition? Explain different steps of holozoic nutrition.

The term ‘heterotroph’ consists of two words ‘hetero‘ and ‘troph‘. ‘Hetero‘ means ‘others’ and ‘troph’ means ‘nutrition’. So, in heterotrophic nutrition the organisms cannot make their own food from carbon dioxide, water and sunlight as they do not have chlorophyll. Such organisms depend on plants directly or indirectly for their food. All the animals, fungi, some protists and bacteria have heterotrophic mode of nutrition.

Heterotrophic nutrition

Such organisms which cannot make their own food and thus depend on other organisms for their food are called heterotrophs. For example, animals, fungi, some protists and bacteria etc.

Test Your Understanding and Answer These Questions:

1. What do you meant by heterotrophs?
2. Write differences between autotrophs and heterotrophs

All the organisms do not have same mode of nutrition, i.e. different organisms have different methods of obtaining and utilizing food. Based on the mode of nutrition, all the living organisms can be classified in two groups:

1. Autotrophic and
2. Heterotrophic

Autotrophic nutrition

The term ‘autotroph‘ consists of two words ‘auto‘ and ‘troph‘. ‘Auto‘ means ‘self‘ and ‘troph’ means ‘nutrition’. So , in autotrophic mode of nutrition the food is manufactured by the organism itself in the presence of sunlight by taking in raw materials such as carbon dioxide or water from the surrounding All the green plants, blue green algae and autotrophic bacteria have autotrophic mode of nutrition.

Such organisms which can make their own food in the presence of sunlight by taking carbon dioxide and water from their surroundings are called autotrophs. Green plants and autotrophic bacteria are the examples of autotrophs. These organisms contain a green colouring pigment called chlorophyll which is capable of trapping solar energy. This solar energy is then used by plants to synthesize food in the form of starch by combining carbon dioxide and water taken from the surrounding by the process of photosynthesis.

It should be noted that green plants are also called producers because they prepare or produce their own food from carbon dioxide and water by using sunlight.

Test Your Understanding and Answer These Questions:

1. What are different modes of nutrition? Explain each by giving one example in each case.
2. What do you meant by autotrophs heterotrophs?
3. Why green plants are called producers?