Cell StructureEdexcel IGCSE Biology: Revision notes
Section 1
What structures are found in cells, and what do they do?
Cells contain several structures, each with a specific function:
| Structure | Function |
|---|---|
| Nucleus | Contains chromosomes (DNA) and controls the cell's activities |
| Cytoplasm | Jelly-like substance where most chemical reactions take place |
| Cell membrane | Controls the movement of substances into and out of the cell |
| Cell wall | Rigid outer layer (made of cellulose in plants) that supports and gives shape to the cell |
| Mitochondria | Site of aerobic respiration, releasing energy for the cell |
| Chloroplasts | Contain chlorophyll and are the site of photosynthesis |
| Ribosomes | Site of protein synthesis |
| Vacuole | Large, fluid-filled space that stores cell sap and helps maintain cell shape/rigidity |
When asked for the function of a structure, always link it to the process it enables, e.g. 'mitochondria are the site of aerobic respiration, which releases energy' rather than just naming the process.
Section 2
How do plant and animal cells differ?
| Structure | Plant cell | Animal cell |
|---|---|---|
| Cell wall | Present (cellulose) | Absent |
| Chloroplasts | Present (in green tissue) | Absent |
| Vacuole | Large, permanent, fluid-filled | Small or absent |
| Shape | Usually fixed, regular shape | Often irregular shape |
| Nucleus, cytoplasm, cell membrane, mitochondria, ribosomes | Present | Present |
Both cell types share the structures needed for basic life processes (nucleus, cytoplasm, cell membrane, mitochondria, ribosomes), but only plant cells have a cell wall, chloroplasts and a large permanent vacuole.
Section 3
Why is cell differentiation important?
Cell differentiation is the process by which a cell develops the specific structures and functions needed to carry out a particular role, becoming a specialised cell. As an organism develops, unspecialised cells differentiate into many different types of specialised cells (e.g. red blood cells, nerve cells, root hair cells), each adapted to carry out a specific job efficiently. This allows multicellular organisms to build tissues and organs made of cells suited to different tasks, rather than every cell trying to do everything.
A root hair cell differentiates to have a long, thin extension that increases surface area for water absorption — a feature not needed by most other plant cells.
Section 4
What are stem cells, and what are the advantages and disadvantages of using them in medicine?
Stem cells are undifferentiated cells that can divide to produce more stem cells or differentiate into a range of specialised cell types.
Advantages of using stem cells in medicine:
- Could be used to replace damaged or diseased cells/tissues (e.g. treating spinal cord injuries, diabetes, some blood disorders)
- Could reduce reliance on organ donors, since new tissue could potentially be grown from a patient's own cells
Disadvantages/concerns:
- Ethical concerns, particularly around the use of embryonic stem cells, which involves destroying an embryo
- Risk of transferring viral infections between donor and recipient
- Risk of rejection by the patient's immune system if cells are not from the patient's own body
- Long-term safety and effectiveness are still being researched
Must Know
- Know both the structure and the function of: nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes, vacuole
- Plant cells have a cell wall, chloroplasts and a large permanent vacuole; animal cells lack these
- Cell differentiation produces specialised cells adapted for specific functions
- Stem cells are undifferentiated and can become many cell types
- Medical use of stem cells offers treatment potential but raises ethical concerns (especially embryonic stem cells) and risks of infection/rejection
That's the notes covered.
Carry on to the next subtopic.