Edexcel iGCSE Biology-1.2 Common Features of Eukaryotic Organisms- Study Notes- New Syllabus

1.2 Variety of Living Organisms – Common Features of Eukaryotic Organisms

📝 Introduction

• When scientists study living things, they group organisms according to their similarities and differences. This makes it easier to understand the huge variety of life on Earth.
• One important group is called eukaryotes.
• Humans, oak trees, mushrooms, and Amoeba may look completely different, but they all belong to this group because their cells share the same basic feature: they contain a nucleus surrounded by a membrane.
• Eukaryotic organisms are generally larger and more complex than prokaryotes (bacteria). Their cells contain specialised structures called organelles, each with a particular job.

🧠 What is a Eukaryote?

A eukaryote is an organism whose cells contain:

• A true nucleus
• DNA enclosed within the nucleus
• Membrane-bound organelles

Examples of organelles include:

Why is the nucleus important?

• The nucleus acts like the control centre of the cell.
• It contains DNA, which carries the instructions needed for:
  • Growth
  • Repair
  • Reproduction
  • Protein production
• Without a nucleus, cells would not be able to control their activities properly.

🌱 Plants

What Are Plants?

• Plants are multicellular eukaryotic organisms that can manufacture their own food through photosynthesis.
• Because they make food instead of consuming other organisms, they are known as producers.
• Plants form the base of almost every food chain and food web on Earth.

Without plants:

• Oxygen levels would fall
• Food chains would collapse
• Most life could not survive

⭐ Characteristics of Plants

1. Plants Are Multicellular

• Plants are made up of many cells.
• These cells work together and become specialised for particular jobs.

Examples:

Why is multicellularity useful?

• Different cells can specialise in different tasks.

This allows plants to:

• Grow larger
• Transport substances efficiently
• Survive in many environments

2. Plants Carry Out Photosynthesis

• Plants contain chloroplasts.
• Inside chloroplasts is a green pigment called chlorophyll.
• Chlorophyll absorbs light energy from the Sun.
• Plants use this energy to produce glucose.

Photosynthesis requires:

• Carbon dioxide from the atmosphere
• Water from the soil
• Light energy from the Sun

Products formed:

• Glucose
• Oxygen

Why is photosynthesis important?

Photosynthesis:

• Provides food for the plant
• Produces oxygen for living organisms
• Forms the basis of food chains

Without photosynthesis, most life on Earth would not exist.

3. Plant Cells Have Cellulose Cell Walls

• Plant cells possess two outer layers:
  • Cell membrane
  • Cell wall
• The cell wall is made from cellulose.

Functions of the cell wall

• Provides support
• Maintains shape
• Prevents bursting when water enters
• Helps plants remain upright

Why is support important?

• Plants cannot move to seek support.
• Therefore, strong cell walls help stems and leaves stay upright and exposed to sunlight.

4. Plants Store Carbohydrates

• Plants produce large amounts of glucose.
• Not all of this glucose is used immediately.
• Excess glucose is converted into storage carbohydrates.

Main storage carbohydrates

• Starch
• Sucrose

Why store food?

Plants need energy:

• During the night
• During winter
• When photosynthesis is not possible

Stored starch acts as an energy reserve.

🌽 Examples of Plants

Maize

• A cereal crop.
• Produces grains
• Rich in starch
• Important food source worldwide

Peas and Beans

• Leguminous plants.
• Produce protein-rich seeds
• Often used in human diets
• Improve soil fertility through nitrogen fixation

🦁 Animals

What Are Animals?

• Animals are multicellular eukaryotic organisms that obtain food from other organisms.
• Because they cannot make their own food, animals are called consumers.
• Animals occupy different positions in food chains.

Examples:

• Herbivores
• Carnivores
• Omnivores

⭐ Characteristics of Animals

1. Animals Are Multicellular

• Animals consist of many specialised cells.
• These cells are organised into:

Cells → Tissues → Organs → Organ Systems

Example:

Muscle cells → Muscle tissue → Heart → Circulatory system

Why is this organisation important?

It allows animals to perform complex activities such as:

• Movement
• Digestion
• Breathing
• Reproduction

2. Animal Cells Have No Chloroplasts

• Animal cells do not contain chloroplasts.
• Therefore, animals cannot photosynthesise.

What does this mean?

• Animals must obtain food by feeding on plants or other animals.
• This is called heterotrophic nutrition.

3. Animal Cells Have No Cell Walls

• Animal cells only possess a cell membrane.

Why is this useful?

Without rigid cell walls:

• Cells remain flexible
• Muscles can contract
• Animals can move

This flexibility is essential for active lifestyles.

4. Animals Show Nervous Coordination

• Animals possess a nervous system.
• The nervous system detects changes in the environment and coordinates responses.

Examples

• Pulling your hand away from a hot surface
• Running from danger
• Catching a ball

Why is nervous coordination important?

It helps animals:

• Survive
• Find food
• Avoid predators
• Reproduce successfully

5. Most Animals Can Move

• Movement is one of the most obvious characteristics of animals.

Animals move to:

• Search for food
• Escape predators
• Find shelter
• Locate mates

Movement increases chances of survival.

6. Animals Store Carbohydrates as Glycogen

• Excess glucose is converted into glycogen.

Glycogen is stored mainly in:

• Liver
• Muscles

Why glycogen?

• Glycogen can be broken down rapidly when energy is required.
• This provides a quick energy source during activity.

🍄 Fungi

What Are Fungi?

• Fungi are eukaryotic organisms that obtain nutrients from organic matter.
• Unlike plants, fungi cannot make food through photosynthesis.
• Many fungi are decomposers and play a crucial role in recycling nutrients.
• Without fungi, dead organisms would accumulate in ecosystems.

⭐ Characteristics of Fungi

1. Fungi Do Not Photosynthesise

• Fungi lack chlorophyll.
• Because they do not contain chlorophyll, they cannot absorb sunlight to make food.
• Instead, they obtain nutrients from existing organic material.

2. Body Made of Hyphae

• Most fungi consist of thin thread-like structures called hyphae.

Hyphae:

• Are long and narrow
• Branch repeatedly
• Contain many nuclei

Why are hyphae useful?

• Their large surface area allows efficient absorption of nutrients.

3. Hyphae Form a Mycelium

• A network of hyphae is called a mycelium.
• The mycelium spreads through food sources.
• This increases contact with the material being digested.

4. Fungal Cell Walls Contain Chitin

• Unlike plants, fungi do not have cellulose cell walls.
• Instead, their cell walls are made of chitin.

Functions of chitin

• Provides strength
• Protects cells
• Maintains shape

5. Saprotrophic Nutrition

• Most fungi feed by saprotrophic nutrition.

Step-by-Step Process

Step 1: Digestive enzymes are released onto food.

Step 2: Food is broken down outside the fungus.

Step 3: Soluble nutrients are absorbed.

This is known as extracellular digestion because digestion happens outside the organism.

Why is this important?

It allows fungi to feed on:

• Dead plants
• Dead animals
• Decaying organic matter

6. Fungi Store Glycogen

• Like animals, fungi store carbohydrates as glycogen.
• This stored glycogen provides energy when needed.

🦠 Protoctists

What Are Protoctists?

• Protoctists are a diverse group of eukaryotic organisms.

Most are:

• Microscopic
• Single-celled
• Aquatic

They do not fit neatly into the plant, animal, or fungal kingdoms.

⭐ Characteristics of Protoctists

1. Usually Single-Celled

• Most protoctists consist of only one cell.

Despite this, a single protoctist can:

• Move
• Feed
• Reproduce
• Respond to its environment

All life processes occur within one cell.

2. Some Are Plant-Like

• Examples such as Chlorella contain chloroplasts.

They can:

• Photosynthesise
• Produce glucose
• Release oxygen

3. Some Are Animal-Like

• Examples such as Amoeba do not contain chloroplasts.
• Instead, they obtain food from their surroundings.
• Amoeba moves using temporary projections called pseudopodia.

4. Some Are Pathogenic

• Certain protoctists cause disease.

A pathogen is a microorganism that causes illness.

Example: Plasmodium

• Plasmodium causes malaria.
• It is transmitted by female mosquitoes.

Why is malaria important?

• Malaria affects millions of people worldwide and remains one of the most significant infectious diseases.

📊Comparison Table

🎯Remember:

• Plants → Cellulose + Starch
• Animals → No Cell Wall + Glycogen
• Fungi → Chitin + Saprotrophic Nutrition + Glycogen
• Protoctists → Usually Single-Celled + Mixed Characteristics