Biology B1

The different parts of the microscope are as follows:

• The eyepiece lens (the bit you look in)
• The body tube
• The rough focusing knob
• The fine focusing knob
• High and low power objective lenses
• Handle
• Stage
• Mirror

Why do we use microscopes?

They allow us to see things that we cannot with the naked eye. For example looking at onion skin allows you to see the cells and the structure of them.

How do we use light microscopes?

• Carry your microscope by the handle.
• Place it near a lamp or window, and angle the mirror so light shines up through the hole in the stage.
• Clip a slide onto the stage. The slid eshould have the object(s) you want to look at stuck to it.
• Select the lowest powered objective lens.
• Turn the rough focusing knob to move the objective lens down to just above the slide.
• Look down the eyepiece lens and adjust the focus using the fine focusing knob.
• Keep adjusting until you get a clear image of whatevers on the slide.
• If you need to see the slide with a greater magnification, switch to a higher powered objective lens.
• Now refocus the microscope.

Parts of the Cell

Most human cell, like animal cells have the following parts:

Parts of a plant cell

'Unspecialised' stem cells can develop into any other type of cell. Stem cells are found in animal zygotes (very young embryos), and in plants of all ages.

Cell Specialisation

A zygote is a structure that forms when sperm fertilises an egg. 

The zygote then divides many times by mitosis to form an embryo. The first division of the zygote forms two cells, the next four, the next eight, and so on.

Up to the eight-cell stage, all of the cells are identical. They are called embryonic stem cells. It is possible for embryonic stem cells to develop into any other specialised type of cell that the growing embryo needs - for example, nerve cells, blood cells and muscle cells. However, once the embryonic stem cells become specialised, they can't change into any other type of cell.

The specialised cells can form all the different types of tissue that the embryo needs.

Enzymes are catalysts produced by living things.

Living things have thousands of chemical reactions going on inside them all the time. These reactions need to be carefully controlled so that you get the right amount of substances.

You can usually make a reaction happen more quickly by raising the temperature. This would speed up the useful reactions but also the unwanted ones too. There's also a limit to how far you can raise the temperature inside a living creature before its cells start getting damaged.

So living creatures produce enzymes which act as biological catalysts. Enzymes reduce the need for high temperatures and you only have enzymes to speed up the usueful chemical reactions in the body.

A CATALYST is a substance which INCREASES the speed of reaction without being  CHANGED or USED UP in the reaction.

Enzymes have special shapes so they can catalyse reactions.

Chemical reactions usuualy involve things either being split apart or joined together. Every enzyme has a unique shape that fits onto the substance invloved in a reaction.

Enzymes are really picky- they usually only catalyse one reaction. This is because, for the enzyme to work, each substance has to fit its special shape.

If a substance doesn's match the enzyme's shape, then the reaction won't be catalysed.

Diffusion is the passive movement of particles from an area of higer concentration to an area of lower concentration.

Diffusion happens in both liquids and gase- that's because the particles are free to moce about randomly. The simplest type is when different gases diffuse through each other, like when the smell of a perfume diffuses through a room. 

Small molecules diffuse across cell membranes.

Membranes hold together a cell.Only very small molecules can diffuse through cell membranes though- things like glucose, amino acids, water, and oxygen. Big molecules like starch and proteins can't fit through the membrane. 

Just like diffusion in air, particles flow through the cell membrane from where there's a higher concentration to where there's a lower conentration. They're only moving about randomly of course, so they go both ways- but if there's a lot more particles on one side of the membrane, there's a net movement from that side. 

Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water conentration to a region of lower water concentration. 

A partially permeable membrane is a membrane that only allows certain substances to diffuse through it. For example, it may only allow water to pass through- not other molecules like starch.

The water molecules actually pass both ways through the membrane during osmosis. This happens because water molecules move about randomly all the time.

But because there are more water molecules on one side than on the other, there's a steady net flow of water into the region with fewer water molecules.

This means the stronger solution gets more dilute. The water acts like it's trying to even up the concentration on eiher side of the membrane.

Osmosis is a type of diffusion- passive movement of water particles from an area of higer water concentration to an area of lower concentration.

Digestive enzymes break down big molecules into smaller ones

Amalyse converts starch into simple sugars. It is made in three places: salivary glands, pancreas, smal intestine

starch amylase enzymemaltose and other simple sugars e.g. dextrins

Protease converts proteins into amino acids. It is made in three places: stomach, pancreas, small intestine

proteinsprotease enzymesamino acids

Lipase converts fat into glycerol and fatty acid. It is made in two places: pancreas, small intestine

fatlipase enzymesglycerol and fatty acids