Year 9 Biology Syllabus Explained: Your Full Guide

In Year 9 Science, you’ll be introduced to the incredible systems that keep life functioning! As part of the Year 9 Biology syllabus, you’ll learn about ecosystems (how animals, plants, and the environment depend on each other) and how your own body keeps you alive.

Table of contents:

• Ecosystems and abiotic factors
• Species interactions
• Matter cycles
• Energy flow
• Homeostasis
• The nervous system
• The endocrine system
• The immune system

This article is part of our Year 9 Science syllabus series. Check out the other articles in the series: Year 9 Chemistry Syllabus and Year 9 Physics Syllabus.

Ecosystems and abiotic factors

The Year 9 Biology syllabus starts with a deep dive into ecosystems. This is where you’ll look at the physical conditions that allow organisms to live and thrive.

Ecosystems include both living (biotic) and non-living (abiotic) components. Abiotic factors are the physical and environmental conditions that affect where and how organisms live. These include:

• Physical features like rocks, soil, and water
• Environmental conditions like sunlight, temperature, wind, and humidity
• Chemical properties like soil pH, salinity, and nutrient or ion levels

Different species are adapted to different conditions. When the abiotic factors suit a species well, its population can grow. When the conditions aren’t right, that species might struggle to survive (or disappear altogether!).

So, are you ready to:

• Identify common abiotic factors?
• Understand and use key terms like salinity, abiotic, and organism?
• Explain how abiotic factors influence where species live and how many survive?

Species interactions

Even if we only focus on living organisms, ecosystems are full of constant interactions:

• Some species compete for the same resources, like a crocodile and a lion fighting over a carcass.
• Others form predator-prey relationships (think birds hunting fish).
• Many cooperate, such as birds that call out to warn others of nearby predators.
• Some organisms act as parasites or spread disease, using other organisms to survive.

These interactions can have surprising effects on population sizes. For example, when wolves were reintroduced to Yellowstone National Park, they ate elk that had been overgrazing young plants and damaging the landscape. With fewer elk, more plants were able to grow, changing the entire ecosystem!

To make sense of these relationships, biologists use tools like food chains and food webs to predict how one species might affect another.

So, are you ready to:

• List different types of interactions between species?
• Explain how these relationships shape ecosystems?
• Use food chains and food webs to model real-world examples?

Get ahead in Year 9 Science!

Your first step into Year 9 Phsyics—test your knowledge with these practice questions

Download now

Get ahead in Year 9 Science!

Fill out your details below to get this resource emailed to you.

"*" indicates required fields

First Name*

Last Name*

Email*

Postcode*

Grade in 2025*

Grade in 2025123456789101112

This field is hidden when viewing the form

Resource (DO NOT DELETE OR CHANGE)

By submitting this form, you agree to receive promotional messages from Matrix about its products and services. You can unsubscribe at any time by clicking on the link at the bottom of our emails.

Matter cycles

All living things depend on certain elements and compounds to survive, especially water, carbon, oxygen, and nitrogen. But if every organism is constantly using these materials, why don’t they run out?

Because matter is recycled through ecosystems.

You’ve probably already learned about the water cycle in earlier years. In Year 9, you’ll focus more on the carbon and nitrogen cycles.

The carbon cycle follows how carbon moves between the atmosphere, living things, and the Earth. For example:

• Plants absorb carbon dioxide from the air during photosynthesis.
• Photosynthesis uses sunlight to convert carbon dioxide and water into glucose (a type of sugar) and oxygen.
• All living things then perform cellular respiration, which breaks down glucose using oxygen to release energy, and produces carbon dioxide and water as by-products.
• These processes can be written as word equations or chemical equations:

Photosynthesis:

carbon dioxide + water (+ sunlight) → glucose + oxygen
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Cellular Respiration

glucose + oxygen → carbon dioxide + water (+ ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

The nitrogen cycle works a bit differently. Nitrogen gas makes up most of the atmosphere, but most organisms can’t use it in that form. Luckily, some types of bacteria can convert nitrogen gas into compounds that plants can absorb through the soil. From there, animals eat the plants and get the nitrogen they need to build proteins and grow.

Many of these cycles rely on microorganisms, especially bacteria and fungi known as decomposers. These organisms break down dead matter into simple chemicals that return to the soil, helping new life to grow. Thanks to this recycling system, ecosystems can reuse essential matter over and over again.

So, are you ready to:

• Explain how matter is recycled in ecosystems?
• Write and understand the equations for photosynthesis and cellular respiration?
• Describe the vital role of microorganisms in nutrient cycles?

Energy flow

Unlike matter, energy is not recycled in ecosystems. Once a living organism uses energy to move, grow, or stay alive, that energy is lost as heat and can’t be reused by other organisms.

Almost all energy on Earth comes from the sun (with small exceptions like geothermal and radioactive sources). The only organisms that can directly convert sunlight into usable food energy are plants. These are called producers because they make their own energy through photosynthesis.

From there, energy flows through a food chain:

• Primary consumers (like herbivores) eat the plants.
• Secondary consumers eat the herbivores.
• Tertiary consumers eat other carnivores.

Because energy is used up at every level (for movement, growth, and basic life functions) only a small portion is passed on to the next level. For example, when a herbivore eats a plant, it only gains access to a fraction of the energy that the plant captured from sunlight. Then, when a carnivore eats that herbivore, it gets even less of the original energy.

This energy loss is shown in an energy pyramid:

As you move up the pyramid, energy decreases, which is why there are fewer top predators than plants or herbivores in most ecosystems.

So, are you ready to:

• Explain the difference between how matter and energy move through ecosystems?
• Classify organisms based on their diet and place in a food chain or food web?
• Use energy pyramids to predict population sizes at each level of the food chain?

Homeostasis

After exploring how ecosystems stay in balance, the next part of the Year 9 Biology syllabus turns your focus inward, to the human body! You’ll be introduced to the concept of homeostasis and explore three key body systems that help maintain it:

• The nervous system
• The endocrine system
• The immune system

What is homeostasis?

Homeostasis is the process your body uses to keep its internal environment stable and suitable for life.

Every minute, your cells are carrying out millions of chemical reactions. For these reactions to work properly, the body needs:

• A constant supply of reactants (like oxygen and glucose)
• The right temperature and pH
• Efficient removal of waste
• Physical protection from damage

Even small changes in internal conditions can be dangerous. That’s why homeostasis keeps things like:

• Blood glucose levels
• Water and oxygen levels
• Carbon dioxide and waste concentrations
• Electrolyte balance and calcium levels
• … within a healthy range.

How does homeostasis work?

Homeostasis relies on feedback loops. These are automatic responses that help the body correct itself if something goes wrong.

For example:

• If your body temperature drops, your body will trigger shivering to create heat.
• If your temperature gets too high, you’ll start sweating, and the evaporation of sweat will help cool you down.

These feedback systems are constantly working behind the scenes to keep you alive and well.

So, are you ready to:

• Define homeostasis in your own words?
• Explain why it’s essential for survival?
• Describe how your body responds to changes using feedback loops?

Nervous system

The next part of the Year 9 Biology syllabus looks at all the different systems in the body. Your nervous system is the body’s main communication network. It monitors your body’s internal conditions and your surroundings—and helps you respond quickly when something changes.

It works by sending electrical signals through specialised cells called neurons (nerve cells). These signals can travel rapidly over long distances, connecting different parts of your body to your brain. Neurons also communicate with each other using special chemicals called neurotransmitters, which makes the system incredibly fast, flexible, and complex.

Structure of a nerve cell

Nerve cells have a unique structure to help them transmit messages efficiently:

• Dendrites receive signals from other neurons.
• The cell body processes the signal.
• The axon carries the signal long distances.
• The axon terminals pass the signal on to the next cell.
• The myelin sheath covers the axon and helps the signal travel faster.
• The nucleus contains the cell’s genetic material and controls its functions.

How does the nervous system work?

The nervous system is made up of three main types of neurons:

• Sensory neurons detect changes in your body or environment (called stimuli)
• Interneurons (mostly in the brain and spinal cord) process the information
• Motor neurons carry signals to your muscles or glands to trigger a response

For example:

• If your body needs more oxygen, your sensory neurons detect low oxygen levels.
• Interneurons process this and send a message through motor neurons.
• Your muscles respond by making you breathe faster.

If the response needs to be slower and longer-lasting (like adjusting your hormone levels), the nervous system passes the message to a gland, which is part of the endocrine system (coming up next!).

So, are you ready to:

• Describe the structure and function of a nerve cell?
• Identify the parts of the nervous system?
• Explain how your body responds to stimuli?
• Understand how the nervous system supports homeostasis?

The endocrine system

When your body needs a long-lasting change, the nervous system sends a message to a gland (part of the endocrine system).

Endocrine glands produce hormones, which are chemical messengers that travel through the bloodstream and affect cells all over the body.

You might have heard of hormones like oestrogen and testosterone, but there are many others that are just as important. Every day, your body releases hormones like:

• Melatonin – makes you feel sleepy
• Insulin – lowers blood sugar
• Glucagon – raises blood sugar
• ADH – helps control urination

Each gland in the body has a specific job. For example:

• The pancreas controls blood sugar
• The thyroid affects metabolism
• The adrenal glands help with the fight-or-flight response
• The pituitary gland is the “master gland” that controls many others

Hormones usually act more slowly than nerve signals, but their effects last longer, making them perfect for steady, ongoing changes.

So, are you ready to:

• Memorise the major glands and the hormones they produce?
• Explain how the endocrine system helps maintain homeostasis?
• Compare how the nervous and endocrine systems control the body?

The immune system

Your immune system protects your body from pathogens. These are harmful organisms that cause disease (like bacteria, viruses, fungi, and parasites).

The immune system has multiple lines of defence:

• Barriers: Your first line of defence includes your skin and stomach acid, which block many pathogens from entering the body.
• Non-specific response: If something does get in, your body sends general defences like white blood cells to destroy invaders or triggers a fever to kill them.
• Specific response: If needed, your immune system produces special white blood cells and antibodies that match the exact pathogen and destroy it more precisely.

Each line of defence works together to keep you healthy and respond to any threat.

So, are you ready to:

• Memorise six types of pathogens and examples of the diseases they cause?
• Explain the three lines of defence in the immune system?
• Reflect on how science and medicine continue to fight disease?

So, are you ready for the Year 9 Biology syllabus?

Biology is one of the most relevant sciences in everyday life. After all, everyone needs their body to work well! By the end of the Year 9 Biology syllabus, you’ll have a strong foundation in the systems that support life. This will set you up for deeper studies in the senior years:

• In Year 10, you’ll study the deeper forces that shape ecosystems and the human body – evolution and genetics.
• In Year 11, you’ll start learning the specific mechanisms that cells use for maintaining homeostasis, looking at plants and animals.
• In Year 12, you’ll dive even deeper into our cell chemistry and genetics, as well as how the many parts of the immune system are shaped by an evolutionary arms race between organisms and their pathogens.

Biology helps us understand the living world, and reminds us just how incredible it is to be alive.