Animal and plant cells
- All living things are made of cells. Some organisms are a single cell (unicellular, such as yeast); others are made of many cells (multicellular).
- Animal cells have a nucleus (controls the cell and contains the genetic material), a cell membrane (controls what goes in and out), cytoplasm (where most chemical reactions happen), mitochondria (where respiration releases energy) and ribosomes (where proteins are made).
- Plant cells have all of these, plus a cell wall made of cellulose (strengthens and supports the cell), chloroplasts (absorb light for photosynthesis) and a permanent vacuole filled with cell sap (keeps the cell firm).
Using a microscope
- Parts: eyepiece lens, objective lenses, stage, light source, coarse focus and fine focus.
- Total magnification = eyepiece magnification × objective magnification. A ×10 eyepiece with a ×40 objective gives ×400.
- Start with the lowest-power objective lens, focus with the coarse focus, then use the fine focus.
- Preparing a slide: put a thin layer of cells (such as onion skin) on a slide, add a stain (iodine for plant cells, methylene blue for cheek cells) and lower a coverslip at an angle to avoid air bubbles.
Specialised cells
- Red blood cells have no nucleus and contain haemoglobin to carry oxygen.
- Nerve cells are long, to carry electrical impulses around the body.
- Sperm cells have a tail to swim and lots of mitochondria to release energy.
- Root hair cells have a long extension that gives a large surface area to absorb water and minerals.
- Palisade cells in leaves are packed with chloroplasts for photosynthesis. Ciliated cells have tiny hairs that sweep mucus out of the airways.
Organisation and science skills
- Cells → tissues (groups of similar cells) → organs (groups of tissues) → organ systems (groups of organs) → organism.
- A hazard is something that could cause harm; a risk is the chance of harm happening. Reduce risks with precautions such as goggles and tying long hair back.
- Units: 1 cm = 10 mm, and 1 mm = 1000 micrometres (µm). Cells are usually measured in micrometres.
- Magnification = image size ÷ actual size.
Key terms
- Cell
- The basic building block of all living things.
- Nucleus
- Controls the cell and contains the genetic material.
- Cell membrane
- Controls what enters and leaves the cell.
- Cytoplasm
- Jelly-like substance where most chemical reactions happen.
- Mitochondria
- Where respiration releases energy.
- Cell wall
- Made of cellulose; strengthens and supports a plant cell.
- Chloroplast
- Absorbs light for photosynthesis.
- Vacuole
- Filled with cell sap; keeps a plant cell firm.
- Specialised cell
- A cell with a special shape or features for its job.
- Tissue
- A group of similar cells working together.
- Organ
- A group of tissues working together.
- Magnification
- How many times bigger an image is than the real object.