CIE iGCSE Biology-1.1 Characteristics of living organisms- Study Notes- New Syllabus
CIE iGCSE Biology-1.1 Characteristics of living organisms- Study Notes – New syllabus
CIE iGCSE Biology-1.1 Characteristics of living organisms- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe the characteristics of living organisms by describing:
(a) movement as an action by an organism or part causing a change of position or place
(b) respiration as chemical reactions in cells breaking down nutrient molecules to release energy for metabolism
(c) sensitivity as the ability to detect and respond to changes in the internal or external environment
(d) growth as a permanent increase in size and dry mass
(e) reproduction as processes making more of the same kind of organism
(f) excretion as removal of waste products of metabolism and excess substances
(g) nutrition as taking in materials for energy, growth and development
Characteristics of Living Organisms – Movement
Movement is one of the seven key characteristics of all living organisms. It refers to an action by an organism or a part of it that results in a change of position or place.
🔍 Key Definition
Movement is the action of an organism or a part of it that results in a change of position or place.
It may involve the whole body or just a part (like a leaf bending or eyes blinking).
Some movements are internal and invisible (e.g., heartbeat or muscle contraction).
Movement in Animals
Animals move from one place to another mainly to find food, escape predators, or reproduce. This whole-body movement is called locomotion.
| Animal | Movement Type | Example |
|---|---|---|
| Human | Muscle + joint action | Running, jumping |
| Fish | Fins and tail | Swimming |
| Birds | Wings | Flying |
| Worms | Muscles only | Crawling |
🌱 Movement in Plants
Plants do not move from place to place, but their parts do show movement in response to light, gravity, touch, or temperature.
| Type of Movement | Example | Trigger |
|---|---|---|
| Phototropism | Shoot grows toward light | Light |
| Geotropism | Roots grow down into the soil | Gravity |
| Nastic movements | Leaves folding in Mimosa | Touch or temperature |
❗ Important Points
- Movement ≠ Locomotion: All locomotion is movement, but not all movement is locomotion.
- Movement can be slow (plant growth) or fast (animal reflex).
- Both internal (heartbeat) and external (walking) movements count.
Movement is a key sign of life. Whether it’s a person running, a fish swimming, or a plant growing toward light – all living organisms show movement to survive and adapt to their environment.
Respiration
Respiration is a life process that occurs in all living cells. It involves a series of chemical reactions that break down food (usually glucose) to release energy for metabolism and other essential body functions.
🧪 Key Definition
Respiration is the chemical reaction in cells that breaks down nutrient molecules to release energy for metabolism.
⚡ Why Do We Need Respiration?
All living organisms need energy to carry out vital life functions such as movement, growth, and temperature regulation.
| Energy Is Needed For… | Example |
|---|---|
| Movement | Walking, flying, swimming |
| Cell division | Growth, tissue repair |
| Temperature control | Keeping warm in humans and birds |
| Sending nerve signals | Thinking and reacting quickly |
| Active transport | Moving substances in and out of cells |
🧫 Where Does Respiration Happen?
Respiration happens in every living cell, inside tiny organelles called mitochondria, known as the “powerhouses” of the cell because they produce energy.
The Basic Respiration Reaction
Aerobic Respiration:
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
C6H12O6 + O2 → CO2 + H2O + Energy
This reaction releases a large amount of energy and is common in animals, plants, and most other organisms.
🧬 What Is Metabolism?
Metabolism is the total of all chemical reactions in the body. Respiration is a vital part of metabolism because it provides the energy required for processes like digestion, protein synthesis, and DNA repair.
❗ Remainder:
| Term | Meaning |
|---|---|
| Breathing | Taking in oxygen and releasing carbon dioxide |
| Respiration | Chemical reaction in cells that releases energy |
Breathing supports respiration by supplying oxygen, but respiration happens inside cells.
Final Recap
Respiration is the invisible engine that powers life – even during sleep. It provides energy for all life processes, and without it, no organism can survive.
Sensitivity
Sensitivity (also called responsiveness) is one of the key characteristics of living things. It is the ability to detect and respond to changes in the environment — either inside or outside the body.
Key Definition
Sensitivity is the ability of an organism to detect and respond to changes in the internal or external environment.
🌍 Why Is Sensitivity Important?
It helps organisms survive, stay safe, and maintain balance (homeostasis).
| Purpose | Example |
|---|---|
| Detect danger | A rabbit hears a predator and runs |
| Maintain balance (homeostasis) | Humans sweat when too hot to cool down |
| Find food | A plant grows toward light (phototropism) |
| React to surroundings | Bacteria move away from harmful chemicals |
🧬 What Is a Stimulus?
A stimulus is any change that causes a response in an organism.
| Type of Stimulus | Example |
|---|---|
| Sound | Loud noise |
| Light | Bright sunlight |
| Temperature | Heat or cold |
| Chemicals | Taste or smell |
| Internal change | Drop in blood sugar or oxygen |
🧠 Human Sensitivity: The 5 Senses
Humans detect stimuli using special sense organs with receptors.
| Sense Organ | Detects… | Receptor Type |
|---|---|---|
| Eyes | Light | Photoreceptors |
| Ears | Sound + balance | Mechanoreceptors |
| Nose | Smell | Chemoreceptors |
| Tongue | Taste | Chemoreceptors |
| Skin | Touch, temperature, pain | Various receptors |
🌱 Sensitivity in Plants
Plants also respond to stimuli, though they don’t have sense organs.
| Response Type | Example |
|---|---|
| Phototropism | Shoots grow toward sunlight |
| Geotropism | Roots grow downward |
| Touch response | Mimosa pudica folds leaves when touched |
Final Recap
Sensitivity keeps organisms aware of their surroundings, helps them stay safe, and maintain internal balance. From blinking to bending toward light – it’s a vital sign of life.
Growth
Growth is a major characteristic of living things. It means getting bigger, heavier, and forming more complex structures through cell division and enlargement.
🔍 Key Definition
Growth is a permanent increase in size and dry mass of an organism, caused by cell division and enlargement.
🧬 How Does Growth Happen?
| Process | Explanation |
|---|---|
| Cell division | New cells are made by mitosis |
| Cell enlargement | Existing cells grow bigger |
| Tissue formation | Cells group to form organs and systems |
Growth in Animals
Growth occurs during early life and slows or stops at adulthood. It involves increasing the number and size of cells, leading to larger tissues and organs.
Example: A baby grows into an adult – taller, heavier, and stronger.
Growth in Plants
Most plants grow throughout life. Growth occurs at special regions called meristems (root and shoot tips).
Example: A seed becomes a tree – taller stem, thicker trunk, more roots and leaves.
🔬 Measuring Growth
- Height or length (e.g., stem height, child’s growth)
- Mass – especially dry mass (removes water weight)
- Number of cells (under a microscope)
💡 Fun fact: Water weight changes daily, but dry mass shows real growth.
⚠️ Growth vs Other Changes
| Not Real Growth | Why Not? |
|---|---|
| A balloon inflating | Temporary, not living |
| Muscles swelling after exercise | Due to water/blood flow |
| Plant wilting | Loss in size, not increase |
Growth is a true sign of life – it means cells are dividing, enlarging, and building the body. Whether it’s a sprouting seed or a growing child – growth means life is active and developing.
Reproduction
Reproduction is a key characteristic of all living organisms. It allows life to continue from one generation to the next and ensures survival of a species.
🔍 Key Definition
Reproduction is the process that makes more organisms of the same kind. It is essential for the survival of a species but not for the survival of an individual.
🧬 Why Is Reproduction Important?
| Reason | Explanation |
|---|---|
| Continues the species | Prevents extinction |
| Creates offspring | New individuals are produced |
| Passes on traits | Genetic information goes from parent to child |
| Allows evolution | Genetic variation leads to adaptation |
🔁 Types of Reproduction
| Type | Features | Examples |
|---|---|---|
| Asexual | One parent, no gametes, clones formed | Bacteria, hydra, some plants |
| Sexual | Two parents, gametes, genetic variation | Humans, animals, flowering plants |
🌿 Asexual Reproduction
- This method involves just one parent. Offspring are genetically identical to the parent (clones). It is common in simple organisms.
- Example: Bacteria dividing by binary fission
- Example: Potato tubers growing into new plants
🧍 Sexual Reproduction
- This method involves two parents and gametes. It results in genetic variation in the offspring, which helps species adapt to changing environments.
- Example: Humans reproducing through fertilisation
- Example: Flowering plants producing seeds after pollination
Final Recap
Reproduction is life’s way of carrying the future forward. It may happen through cloning or combining genes – but its goal is always the same: more life, same kind.
Excretion
Excretion is a vital life process in all living organisms. It involves removing waste products made inside the body during metabolism. These wastes can be harmful if not removed.
🔍 Key Definition
Excretion is the removal of the waste products of metabolism and substances in excess of requirements.
🧪 What Are Metabolic Waste Products?
| Waste Product | Where It Comes From | How It’s Removed |
|---|---|---|
| Carbon dioxide (CO₂) | From respiration in cells | Breathed out through lungs |
| Urea | From breakdown of extra proteins in liver | Removed by kidneys in urine |
| Excess water/salts | From digestion and cell activity | Through urine and sweat |
🚫 What Is NOT Excretion?
| Term | What It Means |
|---|---|
| Excretion | Removal of waste made inside the body |
| Egestion | Removal of undigested food (e.g., feces) |
🧍 How Do Humans Excrete?
| Organ | What It Removes | How |
|---|---|---|
| Lungs | Carbon dioxide and some water | Breathing out (exhalation) |
| Kidneys | Urea, water, excess salts | Urine |
| Skin | Water, salts | Sweat |
🌿 What About Plants?
| Plant Waste Product | How It’s Removed |
|---|---|
| Oxygen | Released during photosynthesis (through stomata) |
| Carbon dioxide | Released during respiration |
| Waste chemicals | Stored in leaves or bark, which fall off |
⚠️ Why Is Excretion Important?
- Toxic substances build up
- Organs get damaged
- Cells stop functioning properly
- It can lead to illness or death
Final Recap
Excretion is the body’s clean-up system. It removes harmful leftovers from chemical reactions so that cells can keep working smoothly. Without it, the body would poison itself from the inside out.
Nutrition
Nutrition is one of the seven essential life processes. It involves taking in materials that the body needs for energy, growth, development, and tissue repair. All living organisms need nutrition, but they get it in different ways.
🔍 Key Definition
Nutrition is the process of taking in materials for energy, growth, and development.
🧬 Why Is Nutrition Important?
| Purpose | Explanation |
|---|---|
| Energy | For movement, warmth, and body functions |
| Growth | Building new cells and tissues |
| Repair | Healing wounds or replacing damaged cells |
| Development | Forming new structures like organs, bones, etc. |
🍽️ Types of Nutrition
| Type | Description | Examples |
|---|---|---|
| Autotrophic | Makes its own food using sunlight (photosynthesis) | Green plants, algae |
| Heterotrophic | Eats other organisms for food | Humans, animals, fungi |
🌿 Autotrophic Nutrition (in plants)
Plants take in carbon dioxide (via stomata), water (via roots), and minerals like nitrates. Using sunlight and chlorophyll, they make glucose through photosynthesis:
Carbon dioxide + Water → Glucose + Oxygen
(in the presence of sunlight and chlorophyll)
Heterotrophic Nutrition (in animals and humans)
Humans and animals take in carbohydrates (for energy), proteins (for growth and repair), fats (for energy storage), vitamins and minerals (for health), and water (for reactions). The food is then digested and absorbed by the body.
⚠️ What If Nutrition Fails?
- No energy → tiredness, fainting
- No growth → stunted body or development issues
- Weak immunity → frequent sickness
- In plants → yellow leaves, stunted growth (mineral deficiency)
Final Recap
Nutrition is life’s fuel station – without it, there’s no energy, no growth, and no survival. Whether it’s a tree making its food or a lion hunting prey – every organism must feed to live.