BIOLOGY

As organisms develop some of the cells

 change and become specialised to carry out •

Particular jobs

This is called differentiation•

Differentiation happens much earlier in the development of

plants than it does in animals•

In plants they may become xylem or root hair cells•

In animals they may become nerve or sperm cells•

animal and plant cells have-

• Nucleus: controls cell activities

• Cytoplasm: where many chemical reactions take place

• Cell membrane: controls the movement of materials

• Mitochondria: where energy is released during aerobic respiration

• Ribosome’s: where proteins are made (synthesised)

Plant cells also have

 • Cell wall: for support

• Chloroplasts: contain chlorophyll for photosynthesis

is the movement of the water a special case of diffusion involving a permeable membrane?

Just like diffusion the movement of molecules is ransom and requires no energy from the cell

Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution to a more concentrate solution

No solute molecules can more across the membrane•

Water is needed to support the cells and because chemical

 reactions take place in the  solution

• Diffusion is the random movement of molecules from an area of high concentration to low Concentration

• The larger the difference in concentration the faster the rate of diffusion

• Examples of diffusion are oxygen in to the cells of the body from the blood stream as the

Cells are respiring

• Also carbon dioxide in to actively photosynthesising plant cells

• Also simple sugars and amino acids from the gut through the cell membranes

• Diffusion does not require any energy from the cell