CB1 - Key Concepts in biology

Function of the lens, focus wheel, stage and slide of a light microscope

Lens - magnifies the image

Focus wheel - changes height of the stage, allows focusing

Stage - where the slide goes

Slide - holds samples for viewing

Differences between light and electron microscopes

Light - image created using light. Can only see to a resolution of 200nm (small bacteria).

Electron - image created using electrons. Resolution of 0.2nm (smaller than viruses).

How to focus a light microscope?

Place the slide on the stage, turn the focus wheel until the image becomes clear.

How to prepare a slide?

Add a thin piece of tissue to the slide, add a stain (iodine / methyl blue), add a coverslip.

How to calculate magnification from eyepiece and objective lens magnifications?

Total magnification = objective lens magnification x eyepiece lens magnification

How to calculate the actual size of something seen through a microscope?

Image size = actual size x total magnification (I=AxM)

How to convert units?

Metres x1000 is millimetres, metres x1000 is micrometres (um), micrometres x1000 is nanometres (nm).

Resolution

Smallest distance between 2 points that can be seen as separate before they seem to become one.

Magnification

The enlargement of the image compared to the original object.

How to convert into standard form?

Move the decimal point of your number until there is only one non-zero digit to the left of the decimal point. Count how many places you moved the decimal point. Write as a x 10 to the power of b (if you moved the point left) or -b (if you moved the point right).

How to draw and label scientific drawings?

Use solid lines- no sketching and no shading

Draw the outline of the cell and organelles

Label with a ruled line and no arrowheads

Describe the function of all the organelles in an animal cell

Nucleus - controls cell, contains genetic information

Cell membrane - controls what goes in and out of the cell

Mitochondria - respiration

Ribosomes - protein synthesis

Describe function of the cell wall, chloroplasts and vacuole

Cell wall - provides structure / support

Chloroplasts - site of photosynthesis

Vacuole - stores water

Difference between prokaryotic and eukaryotic cells

Prokaryotes have no nucleus or other organelles with membranes, eukaryotes have nucleuses and organelles with membranes.

What organelles are found in plants but not animals?

Vacuole, cell wall, chloroplasts

How to tell plant, animal and bacterial cells apart?

Plant - have cell walls and chloroplasts

Animals - no cell wall

Bacteria - no nucleus

Name the gametes

Sperm and egg

Explain the adaptations of sperm

Haploid - has half genetic information Cell membrane

Acrosome - to release enzymes to penetrate jelly coat of the egg

Rail - to swim

Explain the adaptations of egg cells

Haploid - has half genetic information Cell membrane

Jelly coat - will only let one sperm fertilise it

It has a large nutrient rich cytoplasm for the developing embryo

Role and adaptations of ciliated epithelial cells

Have cilia that use energy to waft mucus in the respiratory system and eggs in the oviduct. They have many mitochondria to supply energy for this.

Role and adaptations of digestive cells

Cells lining the intestine have microvilli - tiny folds - that increase surface area for absorption of molecules such as glucose.

Why do dissolved substances diffuse faster through membranes with high surface area?

If the membrane has a high surface area, there is more area for molecules to move through. This increase the rate is diffusion for processes like absorption. Membranes that do this often have folds or projections.

State some specialised plant cells and say how they are specialised

Root hair cell - long projections to increase surface area for absorbing of water.

Palisade cell - in the leaves, with many chloroplasts for photosynthesis.

Describe the function of chromosomal DNA, plasmid DNA, flagellum and slime coat in bacterial cells

Chromosomal DNA - controls the cell

Plasmid DNA - to exchange DNA

Flagellum - for movement

Slime coat - to protect the cell

Units bacteria measured in

Micrometres (um) or nanometres (nm)

Bacteria size compared to plant or animal cells

Bacteria are much smaller than animal or plant cells. They are about the sizes of a mitochondrion in an animal or plant cell.

Enzyme and how it works

A protein that is a biological catalyst. Speeds up reactions without being used up. Allows reactions that would normally take place at higher temperatures happen at lower temperatures by lowering the activation energy if the reaction

When reacting what two things can enzymes do?

Synthesise larger molecules from small ones or break down larger molecules into smaller ones.

How to recognise enzymes in text?

All enzymes end with the letters ‘-ase’

Name some common enzymes and say what they do

Amylase - breaks starch down into glucose - saliva and gut

Catalase - breaks down hydrogen peroxide in cells

Starch synthase - makes starch from glucose

DNA polymerase - makes DNA molecules

Lipase - breaks down lipids

Protease (pepsin) - breaks down proteins

What are proteins, lipids and carbohydrates made of?

Protein - amino acids

Lipids - fatty acids and glycerol

Carbohydrates - made of glucose

Active site

An active site is like a slot on the enzyme where its substrate bonds to it. Substrates and enzymes are specific to each other.

Substrate

The molecule an enzyme binds with and causes to have a reaction (e.g for amylase the substrate is starch).

Describe the lock and key hypothesis

The idea that the shape of the active site fits only one substrate - like a lock and key.

What happens when an enzyme is denatured?

The active site has changed shape and no longer fits the substrate. The enzyme doesn’t work so the reaction doesn’t happen.

What factors affect how rapidly enzymes work?

Temperature, pH and concentration of the substance.

How does temperature affect enzyme activity?

As temperature increases, activity increases, up to the optimum temperature. Above this the enzyme becomes denatured and activity rapidly decreases.

How does pH affect enzyme activity?

At optimum pH, activity is highest - above and below this activity rapidly decreases.

How does concentration affect enzyme activity?

As substrate concentration increases, the activity increases, but then levels off, as all the enzymes active sites are full and cannot react any faster.

What do the effects of temperature, pH and concentration on enzymes look like on a graph?

Temperature - a wave

pH - bell shape

Concentration - steep slope up and level off ( rapid increase then levels off)

Concentration gradient

A difference in concentration of particles between two areas

Diffusion

The movement of particles from an area of their high concentration to an area of their low concentration (down the concentration gradient). Does not require energy.

Osmosis

The movement of water across a partially permeable membrane from an area of low solute concentration to an area of high solute concentration. Does not require energy.

Partially permeable membrane

A membrane that lets through some particles but not others. (E.g cell membrane)

Active transport

The movement of a molecule from an area of its low concentration to an area of its high concentration, using energy

Why do potato chips (and cells) change mass when placed in dilute and concentrated solutions?

In dilute solutions the cells have a higher solute concentration than the surrounding solution so water moves in by osmosis, causing the chip to gain mass.

In concentrated solutions the cells have a lower solute concentration than the surrounding solution so water moves out by osmosis, causing the chip to lose mass.

How to calculate percentage change in mass?

Percentage change = (final mass - initial mass) / initial mass x 100

(This is useful for comparing changes in mass for samples of different initial masses)

Cytoplasm

Gel like substances in the space left in the spell. Anaerobic respiration happens here.