7.
3 Microorganisms and Decay
Key Concepts:
● Microorganisms are tiny organisms that are invisible to the naked eye and
include bacteria, fungi, viruses, and protozoa.
● Decay is the process by which dead organic matter is broken down into
simpler substances, and microorganisms play a key role in this process.
Important Microorganisms in Decay:
● Bacteria: Break down dead plants and animals into simple substances like
carbon dioxide, water, and nutrients.
● Fungi: Decompose organic material and recycle nutrients back into the
environment.
Factors Affecting Decay:
● Temperature: Warmer temperatures generally increase the rate of decay.
● Oxygen availability: Decay tends to occur faster in the presence of oxygen
(aerobic decay).
● Moisture: Moist environments also speed up decay.
● Surface Area: Larger surface area speeds up microbial action as more
material is exposed to microorganisms.
Applications:
● Composting: Microorganisms break down plant waste into humus, which can
be used as a fertilizer.
● Food Preservation: Microbial activity is controlled (e.g., refrigeration or
drying) to prevent decay in food.
7.4 Microorganisms in Food Webs
Key Concepts:
● Food Webs: A food web is a complex network of feeding relationships in an
ecosystem.
● Producers: Organisms (typically plants) that produce their own food through
photosynthesis.
● Consumers: Organisms that feed on other organisms (herbivores, carnivores,
omnivores).
● Decomposers: Microorganisms (bacteria, fungi) that break down dead
organic material and recycle nutrients back into the ecosystem.
Role of Microorganisms:
● Microorganisms (especially decomposers) break down dead plants and
animals, releasing nutrients that are reabsorbed by producers. This forms a
vital part of the food chain and helps sustain ecosystems.
● In the absence of decomposers, dead material would pile up, and essential
nutrients would be unavailable to other organisms.
Unit 4: Grouping and Identifying
Organisms
4.1 Characteristics of Living Organisms
Key Characteristics:
● Movement: All living organisms move in some way, whether it's self-directed
movement or internal movement (e.g., circulation of fluids).
● Respiration: All living organisms require energy, which they obtain through
respiration.
● Sensitivity: The ability to respond to stimuli in their environment.
● Growth: All living organisms grow, either by increasing the number of cells or
by enlarging the size of cells.
● Reproduction: Living organisms reproduce to produce offspring.
● Excretion: The process of removing waste products from the body.
● Nutrition: Living organisms need nutrients for energy, growth, and repair.
4.2 Viruses
Key Concepts:
● Viruses are microscopic infectious agents that cannot live or reproduce
without a host cell.
● They are made of genetic material (DNA or RNA) enclosed in a protein coat.
● Viruses cannot carry out life processes on their own, hence they are often
debated as living or non-living.
● Examples: Influenza, HIV, and the common cold.
Note: Unlike bacteria, viruses are not classified as living organisms because they
cannot reproduce or carry out metabolic processes without a host.
4.3 What is a Species?
Definition:
● A species is a group of organisms that can interbreed and produce fertile
offspring under natural conditions.
● Example: A lion and a tiger can interbreed to produce a liger, but the liger is
typically sterile, meaning lions and tigers belong to different species.
Importance of Species Classification:
● Helps in understanding biodiversity and preserving ecosystems.
● Important for conservation efforts and understanding evolutionary
relationships.
4.4 Using Keys
What is a Key?
● A classification key is a tool used to identify organisms based on their
characteristics.
● Keys use a series of questions with two or more options (dichotomous
questions) to help narrow down the identity of an organism.
Example of a Key:
● Question 1: Does the organism have leaves? (Yes/No)
● Question 2: Is it green? (Yes/No)
4.5 Constructing a Key
Steps for Constructing a Key:
1. Select Characteristics: Choose observable characteristics (e.g., color, number
of legs, presence of wings).
2. Form Questions: Create a series of dichotomous questions (yes/no) based on
these characteristics.
3. Test the Key: Ensure the key can correctly identify all organisms it is meant to
classify.
Example Key for Identifying Simple Organisms:
1. Does the organism have a backbone?
○ Yes → Go to question 2.
○ No → Go to question 3.
2. Does the organism have feathers?
○ Yes → Bird.
○ No → Mammal.
3. Does the organism have a shell?
○ Yes → Mollusk.
○ No → Insect.
Five Kingdoms Classification
Overview of the Five Kingdoms:
1. Animal Kingdom:
○ Multicellular organisms that are heterotrophic (consume food).
○ Examples: Humans, lions, insects.
2. Plant Kingdom:
○ Multicellular, autotrophic organisms (produce their own food via
photosynthesis).
○ Examples: Trees, flowers, moss.
3. Fungi Kingdom:
○ Mostly multicellular (except yeast), heterotrophic organisms that
decompose organic material.
○ Examples: Mushrooms, molds, yeasts.
4. Protist Kingdom:
○ Mostly unicellular organisms that do not fit into the other kingdoms.
Can be autotrophic or heterotrophic.
○ Examples: Amoeba, paramecia, algae.
5. Monera Kingdom:
○ Unicellular organisms, primarily bacteria. They can be autotrophic or heterotrophic
and have no nucleus.
○ Examples: E. coli, blue-green algae (cyanobacteria).
