Types of Cells
All living things are made of cells. The two main types are prokaryotic and eukaryotic cells. The main difference is that eukaryotic cells have a nucleus and other membrane-bound organellesA tiny cellular structure that performs specific functions within a cell (like a mini-organ)..
Eukaryotic Cells (e.g., Plants, Animals)
- Has a 'true' nucleus containing genetic material.
- Contains many different organelles.
- Larger and more complex.
- Examples: plant cells, animal cells, fungi.
Prokaryotic Cells (e.g., Bacteria)
- No nucleus; genetic material (a single DNA loop) floats in the cytoplasm.
- May have smaller rings of DNA called plasmids.
- Much smaller and simpler.
- Example: Bacteria.
Inside Eukaryotic Cells
Animal and plant cells share many components, but plant cells have a few extra parts. Here's a look inside a typical animal cell.
Parts Found in MOST Eukaryotic Cells
Nucleus: Contains the genetic material (DNA) that controls the cell's activities.
Cytoplasm: A gel-like substance where most chemical reactions happen. It contains enzymes that control these reactions.
Cell Membrane: Holds the cell together and controls what goes in and out.
Mitochondria: Where most of the reactions for aerobic respiration take place. Respiration releases energy for the cell to work.
Ribosomes: These are where proteins are made in the cell (protein synthesis).
Parts Found ONLY in Plant Cells
Cell Wall: Made of cellulose. It supports the cell and strengthens it.
Permanent Vacuole: Contains cell sap, a weak solution of sugar and salts. It helps support the plant.
Chloroplasts: Where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll.
Microscopy
Microscopes let us see things that are too small to see with the naked eye. The two main types are light microscopes and electron microscopes.
Key Skill: The Magnification Formula
You need to know how to calculate magnification, image size, or actual size.
Magnification =
Important: Make sure your units for Image Size and Actual Size are the SAME before calculating (e.g., both in micrometres, µm).
Cell Division
Multicellular organisms use mitosis to grow or replace cells that have been damaged. The result is two new cells that are genetically identical to the original cell.
The Cell Cycle & Mitosis
- Growth & DNA Replication: The cell grows and increases its number of sub-cellular structures like mitochondria and ribosomes. It then duplicates its DNA, forming X-shaped chromosomes.
- Mitosis: The chromosomes line up at the centre of the cell and are then pulled apart to opposite ends. The nucleus divides.
- Cytokinesis: The cytoplasm and cell membrane divide to form two identical 'daughter' cells.
Dig Deeper: Stem Cells
A stem cell is an undifferentiated cell that can turn into other types of cells.
Embryonic stem cells can turn into any kind of cell, but using them has ethical issues. Adult stem cells (e.g. from bone marrow) can only turn into certain types, like blood cells.
They could potentially be used to treat conditions like paralysis and diabetes by replacing faulty cells.
Transport in Cells
Substances need to move into and out of cells. This happens in three main ways.
Diffusion
The net movement of particles from an area of higher concentration to an area of lower concentration. It's a passive process, meaning it requires no energy.
Example: Oxygen moving from your lungs into your blood.
Osmosis
The net movement of water molecules across a partially permeable membraneA membrane with very small holes in it. Small molecules (like water) can pass through, but larger molecules cannot. from a region of higher water concentration to a region of lower water concentration.
Active Transport
The movement of substances against a concentration gradientThe difference in concentration between two areas. Particles naturally move 'down' the gradient from high to low. (from low to high concentration). This process requires energy from respiration.
Example: Mineral ions from the soil moving into plant root hair cells.