2.1.2B1. Characteristics of Living Organisms and Cells
Organisation of Cells — Combined Science 0653 - Biology Revision Notes & Topical Questions
5 min read 7 parts Lesson 9 of 14 Unit quiz
Section 1 of 7Making new cells
1Cells divide
- Cells divide New cells are produced when existing cells divide, which is how organisms grow and repair damaged tissue.
2Cells differentiate
- Cells differentiate The new cells develop special features that suit a particular job.
- They become specialised.
3Structure fits function
- Structure fits function The shape and contents of a specialised cell help it to carry out its function efficiently.
Section 2 of 7Specialised animal cells
| Cell | Function | Adaptation |
|---|---|---|
| Ciliated epithelial cell | Moves mucus along the airways | Hair-like cilia on the surface that sweep mucus and trapped particles away |
| Nerve cell (neurone) | Carries nerve impulses around the body | Long axon and branched ends that connect to other cells |
| Red blood cell | Carries oxygen | Biconcave disc shape giving a large surface area, no nucleus so more room for haemoglobin |
| Sperm cell | Carries the male genetic information to the egg | Tail to swim, streamlined head, many mitochondria for energy |
| Egg cell | Is fertilised and supports the early embryo | Large size with a food store in the cytoplasm and a membrane that changes after fertilisation |
Section 3 of 7Specialised plant cells
Root hair cell
- Root hair cell Absorbs water and mineral ions from the soil.
- A long, thin extension from the cell greatly increases the surface area for absorption.
Palisade mesophyll cell
- Palisade mesophyll cell Carries out photosynthesis in the leaf.
- It is tall and packed with chloroplasts, and is found near the top of the leaf where light is strongest.
Section 4 of 7Levels of organisation
1
Cell: the basic unit of life, such as a palisade mesophyll cell or a muscle cell.
2
Tissue: a group of similar cells working together to do a job, for example spongy mesophyll tissue or muscular tissue.
3
Organ: a structure made of several different tissues that work together to perform a function, such as the leaf or the stomach.
4
Organ system: a group of organs that work together, such as the digestive system or the transport system of a plant.
5
Organism: all the organ systems working together make up a whole living thing.
Section 5 of 7Worked example
Identify each level
- Identify each level A leaf contains several tissues that work together for photosynthesis, so it is an organ.
- A palisade mesophyll cell is a single specialised unit, so it is a cell.
- A group of similar spongy mesophyll cells working together is a tissue.
- The correct order from the example, organ then cell then tissue, depends on correct definitions rather than size alone.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Cell division | The process by which a cell splits to form new cells, used for growth and repair. |
| Specialised cell | A cell with a structure adapted to carry out a particular function. |
| Tissue | A group of similar cells that work together to carry out a function. |
| Organ | A structure made of different tissues working together to carry out a function. |
| Organ system | A group of organs that work together to perform a major function in the body. |
Section 7 of 7Exam technique
1
Describing a tissue as a group of different cell types. A tissue is made of similar cells; an organ contains several tissues.
2
Writing the adaptation without linking it to the function, such as saying only that a red blood cell has no nucleus. State that this gives more room for haemoglobin to carry oxygen.
3
Saying that root hair cells absorb sunlight or that palisade cells absorb water. Match each cell to the correct job.
4
Mixing up the order of the levels. It runs from cell to tissue to organ to organ system to organism.
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