The Bio Brief

All living organisms need energy to perform various activities. Even when the body is at rest, energy is required to carry out important life processes such as growth, repair, and maintenance. This energy is obtained from food, which is taken from outside the body

Definition:

Nutrition is the process by which living organisms obtain food and utilize it to get energy, grow, repair body tissues, and maintain life processes.

Why Is Nutrition Necessary?

            •          Provides energy for all life processes

            •          Required even when the body is at rest

•          Helps in growth, development, repair, and synthesis of substances

How Do Living Things Get Their Food?

All organisms require energy and materials, but they obtain them in different ways. Some organisms prepare their own food using simple inorganic substances like carbon dioxide and water. These organisms are called autotrophs.

 Autotrophic Nutrition

            •          Organisms prepare their own food

            •          Use carbon dioxide, water, sunlight, and chlorophyll

            •          Food is usually prepared in the form of glucose

Examples: Green plants, algae, some bacteria

Other organisms depend on complex food materials. These materials must be broken down into simpler substances before use. This process is carried out with the help of enzymes. Such organisms are called heterotrophs.

Heterotrophic Nutrition

            •          Organisms depend on other organisms for food

            •          Food is complex and must be broken down by enzymes

Examples: Animals, fungi, humans

Autotrophic Nutrition:

 Photosynthesis:

Photo means light

Synthesis means to prepare

 What is Photosynthesis?

Photosynthesis is the process by which green plants (autotrophs) make their own food using:

• Carbon dioxide (CO₂)
• Water (H₂O)
• Sunlight
• Chlorophyll

 The food prepared is carbohydrates (glucose), which provide energy to the plant.

Why is Photosynthesis Important?

• Provides food to plants
• Stores energy
• Releases oxygen (O₂) needed by living organisms
• Forms the base of the food chain

Raw Materials Required for Photosynthesis:

Raw Material	Source
Carbon dioxide	Air (through stomata)
Water	Soil (absorbed by roots)
Sunlight	Sun
Chlorophyll	Chloroplasts in green leaves

 Stored Energy in Plants:

• Extra carbohydrates are stored as starch
• Starch acts as the energy reserve of plants
• Similar to glycogen storage in humans

 Steps of Photosynthesis:

 Flowchart: Events in Photosynthesis

Sunlight

   ↓

Absorption of light energy by chlorophyll

   ↓

Conversion of light energy to chemical energy

   ↓

Splitting of water into Hydrogen + Oxygen

   ↓

Carbon dioxide reduced to Carbohydrates (Glucose)

 Three Main Events:

1. Absorption of light energy by chlorophyll
2. Splitting of water into hydrogen and oxygen
3. Reduction of carbon dioxide to carbohydrates

 These steps do not always occur immediately one after the other

Special Case: – Desert Plants

• Take in carbon dioxide at night
• Store it as an intermediate compound
• Use sunlight during the day to complete photosynthesis

Role of Chlorophyll:

• Chlorophyll is a green pigment
• Present in chloroplasts
• Absorbs sunlight
• Essential for photosynthesis

How Does CO₂ Enter the Plant?

 Stomata

• Tiny pores on leaves
• Allow exchange of gases

 Guard Cells Control Stomata

Condition	Guard Cells	Stomata
Water enters	Swollen	Open
Water leaves	Shrunken	Closed

 Stomata close when CO₂ is not needed to prevent water loss

Other Nutrients Needed by Plants:

Nutrient	Importance
Nitrogen	Protein synthesis
Phosphorus	Energy transfer
Iron	Chlorophyll formation
Magnesium	Component of chlorophyll

Nitrogen Absorption:

• Taken as nitrates or nitrites
• Or converted from atmospheric nitrogen by bacteria

Overall Photosynthesis Equation:

Carbon dioxide + Water

   ↓ (Sunlight + Chlorophyll)

Carbohydrates + Oxygen

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Heterotrophic Nutrition

What is Heterotrophic Nutrition?

Heterotrophic nutrition is the mode of nutrition in which organisms cannot make their own food and depend on other organisms for food.

 Animals, fungi, and many microorganisms are heterotrophs.

 Types of Heterotrophic Nutrition:

(A) Saprophytic Nutrition

• Organisms feed on dead and decaying matter
• Food is digested outside the body
• Nutrients are then absorbed

Examples:
 Fungi – bread mould, yeast, mushroom

(B) Parasitic Nutrition

• Organism lives on or inside another organism (host)
• Gets food from host without killing it
• Harms the host

Examples:
 Cuscuta(Amar-bel)
Ticks,lice,leeches
Tapeworm

(C) Holozoic Nutrition

• Food is taken inside the body
• Digested inside
• Common in animals and humans

Examples:
Amoeba, Human beings

 How Do Organisms Obtain Their Nutrition?

Nutrition in Unicellular Organisms

 Nutrition in Amoeba

Steps:

1. Ingestion – Food taken in by pseudopodia
2. Digestion – Food broken down in food vacuole
3. Absorption – Nutrients diffuse into cytoplasm
4. Assimilation – Used for energy and growth
5. Egestion – Undigested food thrown out

 Flowchart: Nutrition in Amoeba

Food captured by pseudopodia

        ↓

Food vacuole formed

        ↓

Digestion inside vacuole

        ↓

Absorption into cytoplasm

        ↓

Undigested food expelled

 Nutrition in Paramecium

• Has a definite shape
• Covered with cilia
• Cilia help move food to a specific spot (oral groove)

 Nutrition in Human Beings (Holozoic Nutrition)

 Alimentary Canal

A long tube from mouth to anus

 Flowchart: Human Digestive System

Mouth

 ↓

Oesophagus

 ↓

Stomach

 ↓

Small Intestine

 ↓

Large Intestine

 ↓

Anus

 Digestion in Different Parts of the Alimentary Canal

(A) Mouth

• Food is chewed by teeth
• Mixed with saliva
• Saliva contains salivary amylase
• Starch → Simple sugars

(B) Oesophagus

• Food pushed by peristaltic movements
• No digestion occurs

(C) Stomach

• Food mixed with gastric juice
• Gastric glands release:
  • Hydrochloric acid (HCl) – kills germs & activates pepsin
  • Pepsin – digests proteins
  • Mucus – protects stomach lining

 Excess acid causes acidity

(D) Small Intestine (Main Site of Digestion)

• Long and highly coiled
• Receives:
  • Bile juice (from liver)
  • Pancreatic juice (from pancreas)
  • Intestinal juice

Functions:

• Complete digestion of:
  • Carbohydrates → Glucose
  • Proteins → Amino acids
  • Fats → Fatty acids + Glycerol

 Role of Bile Juice

• Makes food alkaline
• Breaks fats into small droplets (emulsification)

(E) Absorption of Food

• Small intestine has villi
• Villi increase surface area
• Nutrients absorbed into blood

(F) Large Intestine

• Absorbs water
• Forms faeces

(G) Anus

• Undigested waste removed
• Controlled by anal sphincter

Difference in Digestive System

Animal	Food Type	Small Intestine
Herbivores (cow)	Plant food	Long
Carnivores (lion)	Meat	Short

 Dental Caries (Tooth Decay)

Causes:

• Bacteria act on sugars
• Produce acid
• Acid damages enamel

Process:

Sugary food

   ↓

Bacteria produce acid

   ↓

Enamel weakens

   ↓

Tooth decay

Prevention:

• Brush teeth regularly
• Remove dental plaque
• Maintain oral hygiene