ANAND CLASSES study material and notes to learn about the Modes of Nutrition in organisms, including Autotrophic Nutrition (photosynthesis and chemosynthesis) and Heterotrophic Nutrition (holozoic, saprophytic, and parasitic). This detailed guide is essential for Class 10 Science Biology students preparing for CBSE, JEE, and NEET exams.
Modes of Nutrition
Modes of nutrition refer to the various ways through which organisms procure food. Nutrition is essential for the survival, growth, and energy requirements of all living organisms. Different organisms have evolved different methods to obtain nutrients based on their environmental conditions and biological structures.
All organisms can be broadly classified into two major categories based on their mode of nutrition:
- Autotrophic Nutrition (Self-sustaining nutrition)
- Heterotrophic Nutrition (Dependent nutrition)
Each of these categories is further divided into various subtypes, which we will explore in detail.
1. Autotrophic Mode of Nutrition
Definition
The term ‘autotrophic’ is derived from the Greek words ‘auto’ meaning ‘self’ and ‘trophe’ meaning ‘nutrition’. Hence, autotrophic nutrition refers to self-nutrition, where organisms synthesize their own food from inorganic materials like carbon dioxide and water using an external source of energy.
Characteristics of Autotrophic Nutrition
- Organisms prepare their own food.
- Requires inorganic substances like CO2 and H2O.
- Energy is derived from sunlight (photosynthesis) or chemical reactions (chemosynthesis).
- Found in green plants, algae, and some bacteria.
Types of Autotrophic Nutrition
1. Photosynthetic Autotrophs
- These organisms utilize sunlight to prepare food via the process of photosynthesis.
- Chlorophyll, a green pigment present in plants, absorbs sunlight and helps convert inorganic substances into organic food.
- Oxygen is released as a byproduct of photosynthesis.
Photosynthesis: The Process of Food Synthesis
Photosynthesis occurs in the chloroplasts of green plants. It is a complex biochemical process where light energy is converted into chemical energy. The generalized chemical equation for photosynthesis is:
$$6CO_2 + 6H_2O + Sunlight \rightarrow C_6H_{12}O_6 + 6O_2$$
This means that plants take in carbon dioxide (CO2) and water (H2O) from their surroundings and, with the help of sunlight, convert them into glucose (C6H12O6), which serves as food. Oxygen (O2) is released into the atmosphere as a byproduct.
Examples: Green plants (mango tree, grass, rose plant), algae (Spirogyra, Chlorella), cyanobacteria.
2. Chemosynthetic Autotrophs
- These organisms use chemical energy to prepare food instead of sunlight.
- They obtain energy by oxidizing inorganic substances like hydrogen sulfide (H2S), ammonia (NH3), and iron compounds.
- Found in deep-sea hydrothermal vents and extreme environments.
Examples: Nitrifying bacteria (Nitrosomonas, Nitrobacter), sulfur bacteria.
2. Heterotrophic Mode of Nutrition
Definition
The term ‘heterotrophic’ is derived from ‘heteros’ meaning ‘others’ and ‘trophe’ meaning ‘nutrition’. In this mode, organisms depend on others for food as they cannot synthesize their own food.
Characteristics of Heterotrophic Nutrition
- Organisms cannot produce their own food.
- They rely on plants or other animals for nutrition.
- Found in all animals, fungi, and most bacteria.
Types of Heterotrophic Nutrition
1. Holozoic Nutrition
- Organisms ingest solid food, digest it internally, absorb nutrients, and excrete waste.
- Occurs in most animals, including humans.
Examples: Humans, dogs, cats, lions.
2. Saprophytic Nutrition
- Organisms obtain nutrients from dead and decaying organic matter.
- They release digestive enzymes outside their body to break down food externally before absorbing nutrients.
Examples: Fungi (mushrooms), bacteria (decomposers).
3. Parasitic Nutrition
- Organisms live on or inside a host and obtain nutrients at the host’s expense.
- The host is harmed but may not always die immediately.
Examples: Tapeworms, lice, Cuscuta (Amarbel).
Question-Answer for Class 10 CBSE Board Exam
Q1: What is the major difference between autotrophs and heterotrophs?
A: Autotrophs synthesize their own food from inorganic substances, while heterotrophs depend on other organisms for food.
Q2: Why are green plants considered autotrophs?
A: Green plants contain chlorophyll, which allows them to synthesize food using sunlight through photosynthesis.
Q3: Give an example of an autotrophic bacterium.
A: Cyanobacteria (blue-green algae) are autotrophic bacteria capable of photosynthesis.
Conceptual Questions
Q1: How does photosynthesis help in the survival of heterotrophic organisms?
A: Photosynthesis produces organic food and oxygen, which are essential for heterotrophic organisms’ survival.
Q2: Explain why fungi are considered saprophytes.
A: Fungi obtain nutrition from decomposing organic matter, making them saprophytic in nature.
Do You Know?
- Some bacteria use chemical energy instead of sunlight to make food. This is called chemosynthesis.
- Venus flytrap and pitcher plants are examples of plants that exhibit both autotrophic and heterotrophic nutrition.
- Mycorrhiza is a mutualistic association between fungi and plant roots that helps in nutrient absorption.
Worksheet
Fill in the Blanks:
- _______ are organisms that produce their own food using sunlight energy.
- The pigment responsible for photosynthesis is called _______.
- Humans exhibit _______ mode of nutrition.
- _______ obtain nutrients from dead and decaying matter.
True or False:
- All bacteria are autotrophs. (____)
- Fungi exhibit saprophytic nutrition. (____)
- Autotrophs depend on other organisms for food. (____)
Test Paper (10 Marks)
Q1: Define autotrophic and heterotrophic nutrition. Give two examples of each. (2 Marks)
Q2: Explain the process of photosynthesis with a balanced chemical equation. (3 Marks)
Q3: Differentiate between saprophytic and parasitic nutrition. (2 Marks)
Q4: Why are humans considered holozoic organisms? (1 Mark)
Q5: Name a plant that shows both autotrophic and heterotrophic nutrition. (1 Mark)
Q6: What is chemosynthesis? Give an example. (1 Mark)
Quick Revision Points
✔️ Nutrition is the process by which organisms obtain food and energy for survival.
✔️ Autotrophs synthesize their own food, whereas heterotrophs depend on other organisms.
✔️ Photosynthesis is the process by which autotrophs convert sunlight, CO₂, and H₂O into food.
✔️ Heterotrophs include herbivores, carnivores, omnivores, parasites, and saprophytes.
✔️ Fungi and most bacteria obtain nutrition through decomposition of organic matter.
✔️ Some bacteria perform chemosynthesis instead of photosynthesis.
🔷 Best Coaching Center for IIT-JEE, NEET, and Foundations
🔹 ANAND CLASSES – The best coaching institute for JEE, NEET, and Class 11-12 Foundations.
🔹 Buy complete study material at 👉 https://publishers.anandclasses.co.in/
🔹 Proprietor: NIRMAL ANAND Educations
🔹 Written by: Neeraj Anand
🔹 Published by: Anand Technical Publishers under Anand Classes
📞 Contact: +91-9463138669
📧 Email: anandclasses1996@gmail.com
