Transport and Interactions in Living Systems
Cells must move substances in and out to stay alive. Meet diffusion, osmosis and active transport, see why large organisms need exchange surfaces and transport systems, then follow the energy through a food chain and look at human impact on biodiversity.
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Getting substances in and out
Every living cell has to take in what it needs, such as oxygen and food, and get rid of waste, such as carbon dioxide. Substances cross the cell membrane in three main ways. A tiny organism can rely on substances simply spreading in and out, but a large organism needs special exchange surfaces and transport systems to move materials over bigger distances.
Three ways substances move
Learn these four terms. The first three are the ways a substance can cross a cell membrane. The fourth is the special membrane that lets some things through but holds others back.
Match the process to its meaning
- Diffusion
- Osmosis
- Active transport
- Concentration gradient
- Particles spread from a high to a low concentration, with no energy needed
- Water moves across a partially permeable membrane to the more concentrated side
- A substance is pumped against the gradient using energy from respiration
- The difference in concentration between two regions that substances move down
Which process is this?
A plant root takes in water from the soil. The water crosses a partially permeable membrane, moving from the dilute soil water into the more concentrated cell. Which process is happening?
- Osmosis
- Diffusion
- Active transport
- Respiration
Passive or active?
Diffusion and osmosis are passive: substances move down the concentration gradient and no energy is needed. Active transport is different: it moves substances the other way, against the gradient, so it must use energy released by respiration.
Complete the transport vocabulary
In _____, particles spread from a high to a low concentration. The movement of water across a partially permeable membrane is called _____. Moving a substance against its gradient is called _____, and only this process uses _____ from respiration. A good exchange surface is thin and has a large surface _____.
A good exchange surface
Which features help a surface exchange substances quickly? Choose all that apply.
- A large surface area
- A thin surface, so the distance is short
- A good blood supply to keep the gradient steep
- A thick, waterproof outer layer
- Being as small as possible
Spot the true statements
An interactive activity.
Why size matters
In a tiny single-celled organism, substances only travel a short way, so diffusion alone is fast enough. In a large organism the inner cells are far from the surface, and diffusion would be far too slow. That is why large organisms have exchange surfaces such as lungs and gills, and transport systems such as the blood, to carry substances the long distances.
Order the food chain
An interactive activity.
Match the ecosystem role
- Producer
- Primary consumer
- Decomposer
- Biodiversity
- A green plant or alga that makes its own food by photosynthesis
- An animal that eats producers, so it is a herbivore
- A bacterium or fungus that breaks down dead organisms
- The variety of different species living in an ecosystem
What do the arrows show?
In a food chain, the arrows point from one organism to the next. What do these arrows represent?
- The flow of energy from one organism to the next
- The order in which the animals were born
- Which organism is the largest
- The direction the animals move in
Name the process
An interactive activity.
Explain how substances enter a cell
An interactive activity.