Cells and organisation, Year 7: more practice

A tissue

提示It sits between a single cell and a whole organ in size.

为什么Muscle tissue is made of muscle cells that all contract. Different tissues then combine to form an organ such as the stomach.

An organ system

提示Your stomach and gut belong to one such group.

为什么The heart, blood vessels and blood form the circulatory system. Systems working together make up the whole organism.

The cytoplasm

提示It fills the space between the cell membrane and the nucleus.

为什么Cytoplasm is mostly water. Many of the cell's chemical reactions happen in it, and the other parts of the cell are held in it.

Cell wall, chloroplasts and a large permanent vacuole

提示One part supports, one catches light and one is full of sap.

为什么The wall gives support, the chloroplasts carry out photosynthesis and the vacuole stores cell sap and keeps the cell firm.

It can carry electrical messages over long distances around the body

提示Think about what the cell must reach.

为什么Nerve cells carry electrical impulses between the brain and the rest of the body. Their long fibres let one cell link places far apart.

They release lots of energy for the muscle to contract

提示Think about the fuel a working fibre needs.

为什么Mitochondria are where respiration releases energy. A muscle cell that contracts again and again needs a plentiful supply.

Diffusion

提示Particles spread out from where there are lots of them.

为什么Scent particles leave the food, where they are crowded, and move randomly into the rest of the air where there are few.

It speeds up because the particles move faster

提示Think about what warmth does to how fast tiny pieces travel.

为什么At higher temperatures particles have more kinetic energy, so they spread out faster. This is why a smell reaches you sooner in a warm room.

100

提示Divide the drawing size by the real size.

为什么Magnification = image size ÷ real size = 5 ÷ 0.05 = 100, written ×100.

0.8 mm

提示Rearrange the formula so the real size is the subject.

为什么Real size = image size ÷ magnification = 40 ÷ 50 = 0.8 mm.