Revision

Diffusion - is the net movement of particles from an area of high concentration to an

area of low concentration, along a concentration gradient.

Osmosis - is the net movement of water from a dilute solution to a more concentrated

solution through a partially permeable membrane.

Active transport (1) - is when molecules move against the concentration gradient, from

an area of low concentration to an are of high concentration. This

requires energy.

Active transport (2) - Is the movement of glucose (sugar) from an area of low

concentration to an area of high concentration through a carrier

protein by using ATP (energy). The glucose enters the protein and

rotates, then it is released into the cell. (3 marks)

• Oxygen and glucose move into the cells by diffusion. Carbon dioxide moves out of the cell by diffusion.
• A concentration gradient is a measurement of how the concentration of something changes from one place to another.
• Glucose is moves from the intestine into the bloodstream by active transport. Minerals of from the soil move into the root hair cells by active transport.
• A dilute solution has high water potential. A concentrated solution has low water potential. In osmosis, water diffuses from a region of high water potential to a region of low water potential.
• There are ethical issues about the use of stem cells. E.g 'is it right to destroy many embryos life?' Or 'is it right to dispose of human embryos?' and 'who decides which people should benefit from this treatment?'.

Mitosis is the division of cells to make new cells. New cells are needed because the old ones have either died or are damaged. The growth and division of cells is called the cell cycle.

The 5 stages of mitosis are

• parent cell contains chromosomes
• chromosomes are copied
• the chromosome slime up in the middle
• chromatids (the 2 sets of chromosomes) pull apart
• the 2 new cells are created, each of them are identical to the parent

Cell differentiation occurs when one cell changes into another type of cell. In animals, this usually happens at an early stage of development and occurs to create specialised cells. In mature animal cells, differentiation is mostly restricted to replacement and repair. Many plant cells, however, maintain the ability to differentiate .

Here are some of the specialised cells:

Root hair cells - tiny-hair like extensions increase the surface area of the cell for absorption.

Ovum (egg cell) - large cell that can carry food reserves for the developing embryo.

Xylem - long, thin, hollow cells used to transport water through the stem and root.

Sperm cell - has a tail which allows it to move.

Nerve cell - has long, slender axons that carry nerve impulses.

• Stem cells are undifferentiated cells that can differentiate to form specialises cells,

such as muscle cells or nerve cells.

• Human stem cells can come from human embryos, in the umbilical cord blood from

new born babies or from adult bone marrow.

• Embryonic stem cells can differentiate into any type of cell
• Adult stem cells can differentiate into the cells of the type of tissue they came from.
• Plant stem cells are found in meristematic tissue, which is usually in the tips of shoots

and roots.

• Stem cells have the potential to provide replacement cells and tissues to treat

Parkinson's disease, burns, heart disease and arthritis. The tissues made will not be

rejected by the body.

• Stem cells can also be used for testing new drugs.