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Diffusion, single cells and body organisation
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Cells take in what they need by diffusion. Some living things are just one cell; others are built from billions of cells working together.
Diffusion
Diffusion is the spreading out of particles from where there are lots of them (high concentration) to where there are fewer (low concentration).
Oxygen diffuses into cells for respiration. Carbon dioxide diffuses out.
It happens on its own: no energy is needed.
Oxygen diffuses into cells for respiration. Carbon dioxide diffuses out.
It happens on its own: no energy is needed.
Unicellular organisms
A unicellular organism is made of one cell, which must do everything.
Amoeba: changes shape and pushes out parts of the cell to move and to surround its food.
Euglena: has a whip-like flagellum to swim, chloroplasts to make food, and an eyespot that helps it swim towards light.
Amoeba: changes shape and pushes out parts of the cell to move and to surround its food.
Euglena: has a whip-like flagellum to swim, chloroplasts to make food, and an eyespot that helps it swim towards light.
From cells to organisms
In a multicellular organism, cells are organised in levels:
cell → tissue → organ → organ system → organism
A tissue is a group of similar cells (muscle tissue). An organ is made of several tissues (the heart). An organ system is organs working together (the circulatory system).
cell → tissue → organ → organ system → organism
A tissue is a group of similar cells (muscle tissue). An organ is made of several tissues (the heart). An organ system is organs working together (the circulatory system).
Put these in order from smallest to largest: organ, cell, organism, tissue, organ system.
- The smallest unit is the cell.
- Similar cells make a tissue; tissues make an organ.
- Organs make a system; systems make the organism.
Answer: cell, tissue, organ, organ system, organism
Diffusion: particles spread from high to low concentration. Unicellular organisms like amoeba and Euglena have features to move and feed. Cell, tissue, organ, organ system, organism.
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