Life Processes- Class X Science Notes (Part 1- Nutrition in Plants)

• Nutrition:  The process by which an organism takes in food and uses it for energy, growth, and repair is called nutrition. 
• Need for Nutrition: The need for nutrition arises when organisms require energy to carry out their various activities. The energy is supplied by nutrients which provide the raw materials that the organisms need for growth and repair. 
• Nutrients: Nutrients are substances that are necessary for the growth and health of organisms.

Types of Nutrients:

1. Macronutrients: Macronutrients (carbohydrates, proteins, and fats) are essential nutrients which are needed by organisms to survive.
2. Micronutrients: Micronutrients (minerals and vitamins) are required in very small amounts and are not essential to the survival of organisms.

Modes of Nutrition:

1. Autotrophic Nutrition.
2. Heterotrophic Nutrition.

Autotrophic Nutrition: The mode of nutrition in which an organism prepares their own food (nutrients) is called autotrophic nutrition. Green plants and blue-green algae are some examples.

• Autotrophs: Organisms (such as green plants) which carry out autotrophic nutrition are called autotrophs.

Nutrition in Plants: Green plants make their own food using sunlight. Sunlight provides energy and carbon dioxide and water are the raw materials. The chloroplast is the site where food is made.

Photosynthesis: Photosynthesis is the process by which plants use sunlight and water to convert carbon dioxide and water into carbohydrates.

• During this process, the energy from the sun(solar energy) is converted into chemical energy and carbohydrates are produced.
• Photosynthesis takes place in leaves.
• The green part of the plant contains a pigment that is made up of chloroplasts, chlorophyll (a pigment that is green).
• The process of photosynthesis is commonly written as: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. 

Raw Materials for Photosynthesis:

1. Sunlight
2. Water, H₂O
3. Carbon dioxide, CO2
4. Chlorophyll

Main Events of Photosynthesis:

• Absorption of light energy by chlorophyll.
• The conversion of light energy into chemical energy and the splitting of water into hydrogen and oxygen are both processes that occur naturally.
• Conversion of carbon dioxide into carbohydrates (reduction).
• The sunlight helps to activate the chlorophyll, which results in the splitting of the water molecule.
• The hydrogen released by the splitting of a water molecule is used to reduce carbon dioxide to produce carbohydrate.
• Oxygen is a by-product of photosynthesis.
• Carbohydrates are turned into starch and stored in various parts of the plant.
• The splitting of water molecules is an important part of the light reaction.
• photosynthesis occurs in two phases – light reaction and dark reaction.

Light Reaction

 Definition: The light reaction is a chemical process that happens as a result of light absorption (light dependent) and produces different molecules, such as ATP and NADPH.

       The light reaction of photosynthesis only initiates when light energy is supplied.  

Dark Reaction

Definition: The dark reaction is a light-independent process in which sugar molecules are formed from the carbon dioxide and water molecules.

      The dark reaction occurs in the cell's interior(stroma of the chloroplast), where they use the products of the light reaction.

Significance of Photosynthesis:

• Photosynthesis is a process through which solar energy is made available to different living beings.
• The process of photosynthesis helps to maintain the balance of carbon dioxide and oxygen in the air.
• All organisms in an ecosystem need food in order to survive. Green plants are the main producers of food in the ecosystem, and all other organisms rely on them directly or indirectly  for sustenance.

Stomata

          The stomata are tiny pores on the epidermis of leaves and stems that allow for gas exchange and transpiration.

Functions of stomata

• The stomata on a plant's leaves are responsible for transpiration and the removal of water vapor (excess water).  
• It help in the gaseous exchange between the plant and surrounding.
• The night time closure of the stomata prevents water from escaping through the pores.
• The stomata on the leaves of plants facilitate the uptake and release of oxygen during the process of photosynthesis.

Heterotrophic Nutrition: The mode of nutrition in which an organism uses to obtain food from another organism is called heterotrophic nutrition. This can be further divided into three categories: saprophytic, holozoic, and parasitic.

• Saprophytic Nutrition: In saprophytic nutrition, the organism consumes the decomposed food. The food is digested while it is still in the organism's mouth. The digested food is then swallowed by the organism. All decomposers follow this form of nutrition. Some insects, like houseflies, also follow this mode of nutrition.
• Holozoic Nutrition: In holozoic nutrition, the digestion of food occurs in the body of the organism after it has been ingested. Most of the animals follow this mode of nutrition.
• Parasitic Nutrition: Parasitic nutrition refers to the process by which an organism obtains its nutrition from another organism living within or outside of it. This type of nutrition is often called parasitic because the organism living off of the host's resources derives a benefit from it. For example, ticks, which feed on blood, are classified as parasites.

Nutrition in Amoeba

• Amoeba is an unicellular organism which follows the holozoic mode of nutrition.
• In holozoic mode of nutrition, the digestion of food follows after the ingestion of food. Thus, the digestion takes place inside the body of an organism.
• Holozoic nutrition occurs in five steps: ingestion, digestion,  absorption, assimilation and egestion.

Steps of Holozoic Nutrition:

1. Ingestion: The process of consuming food is known as ingestion.
2. Digestion: The process of breaking down complex food molecules into simpler ones so that they can be absorbed into the body is called digestion.
3. Absorption: The process of absorbing food that has been digested is called absorption.
4. Assimilation: The process of using digested food to provide energy and grow and repair body tissues is called assimilation.
5. Egestion: The process of removing undigested food or waste material from the body is called egestion.

Amoeba uses the holozoic mode of nutrition. This means that the cell membrane of the amoeba continuously protrudes into pseudopodia. These pseudopodia surround food particles and form a food vacuole. This vacuole contains the food particle and water, and the amoeba's digestive enzymes are secreted into it. After digestion takes place, the food vacuole moves away from the cell membrane, and the amoeba expels the undigested food.