Cell biology
Eukaryotic and prokaryotic cells
Plant, animal and fungal cells are all eukaryotic.
Bacterial cells are prokaryotic
Prokaryotic cells
Cells are much smaller in size and the genetic material is not enclosed in a nucleus.
In prokaryotic cells the genetic material is a single DNA loop and there may be one or more small rings of DNA, called plasmids.
Eukaryotic cells
They have cytoplasm and a cell membrane surrounded by a cell wall.
They have a cell membrane, cytoplasm and genetic material enclosed in a nucleus
HAS A NUCLEUS
HAS NO NUCLEUS
Animal and plant cells
Animal
All cells have structures inside them called sub-cellular structures.
The sub cellular structures include:
A nucleus which controls the cell and contains the genetic material
Cytoplasm where most of the chemical reactions take place
cell membrane which controls the passage of substances into and out of the cell.
Mitochondria where aerobic respiration takes place
Ribosomes, where proteins are synthesised (made)
Plant
Plant cells contain all the sub- cellular structures found in animal cells.
They also have:
A cell wall made of cellulose which strengthens the cell.
A permanent vacuole filled with cell sap, which supports the plant.
Plants need to make their own food, so some of their cells contain chloroplasts.
Chloroplasts absorb light to make food (glucose) by photosynthesis
Microscopy
In order to study cells microscopy skills have developed over time and electron microscopy has increased understanding of sub cellular structures.
Magnification= size of image ÷ size of real object
An electron microscope has much higher magnification and resolving power than a light microscope. this means that it can be used to study cells in much finer detail.
Cell division- mitosis
Cells go through a series of changes involving growth and division, called the cell cycle.
One of the stages is mitosis, when the cell divides into two identical cells.
Before a cell can divide it needs to grow and increase the number of sub-cellular structures, such as ribosomes and mitochondria.
The DNA then replicates to form two copies of each chromosome. In this way the genetic material is doubled.
During mitosis:
One set of chromosomes is pulled to each end of the cell.
The nucleus divides
The cytoplasm and cell membranes divide to form two identical cells.
Cancer
Cancer is the result of changes in cells that lead to uncontrolled growth and division.
Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body.
Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours.
Scientists have identified lifestyle risk factors for various types of cancer.
There are also genetic risk factors for some cancers.
Diffusion, osmosis and active transport
Diffusion
Diffusion is movement of particles from an area of higher concentration to an area of lower concentration.
Substances may move into and out of cells across the cell membranes via diffusion
Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange
Factors which affect the rate of diffusion are:
• the surface area of the membrane.
• the temperature
• the difference in concentrations (concentration gradient)
Osmosis
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
Water may move across cell membranes via osmosis.
Active transport
Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient).
This requires energy from respiration.
Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil.
Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.