Cells

Question 1

Cytoplasm (Or cytosol)

Answer 1

Contains enzymes for metabolic reactions

Also contains amino acids, salts and sugars

Question 2

Nucleus

Answer 2

Contains hereditary material

Produces RNA (mRNA, tRNA, rRNA)

Controls the activities of the cell

Contains nuclear pores to allow substances (mostly mRNA) in and out of the cell

Question 3

Mitochondria

Answer 3

Site of aerobic respiration

ATP formed

Double membrane

Inner membrane = highly folded = cristae
This increases surface area to fit more enzymes so faster respiration

Inside cristae there is a fluid called matrix - Contains DNA and ribosomes

Question 4

Ribosome

Answer 4

Protein Synthesis

Smallest organelle in the cytoplasm

80S in eukaryotic and 70S in prokaryotic

Question 5

Endoplasmic Reticulum

Answer 5

Join to the nuclear envelope, layers of flattened sacs called cisternae

Question 6

Rough endoplasmic reticulum

Answer 6

Encrusted with ribosomes that synthesise proteins

Question 7

Smooth endoplasmic reticulum

Answer 7

No ribosomes

Synthesises stores and transports lipids and carbohydrates

Question 8

Gulgi apparatus/vesicles

Answer 8

Multiple flattened sacs form cristanae

Products from ER pass through it

Modifies substances and packages them into golgi vesicles

Also make lysosomes

Finished products transported to cell surface in golgi vesicles where they fuse with the membrane and are released

Question 9

Lysosomes

Answer 9

Produced by the golgi apparatus

Sacs surrounded by a single membrance

Contain hydrolytic enzymes (enzymes that break down biological molecules)

Destroy unwanted chemical, worn out organelles, engulfed viruses/bacteria, dead cells (autolysis)

Products then recycled to synthesise new substances

Question 10

Chloroplasts

Answer 10

Double membrane which is high selective

A thylakoid is a single disc containing chlorophyll

A granum is stacks of thylakoids

Lamella connect granum together

Question 11

Stoma

Answer 11

Fluid filled matrix where sugars are synthesised during photosynthesis. Enzymes and starch grains often found here

Question 12

Vacuole

Answer 12

Contains a solution of salt, sugar and amino acids (makes cells turgid)

Question 13

What is the cytoplasm of a bacterial cell made of

Answer 13

Peptidoglycan and murein

Question 14

Light microscope

Answer 14

Limited by x1500

Allows individual cells and some larger structures such as the nucleus to be observed but no smaller structures

Resolution is approximately 0.2 micrometres

Question 15

Why do light microscopes have a low resolution

Answer 15

Light microscopes have a long wavelength of light

Electrons are used to increase resolution as they have much shorter wavelength

Question 16

How an electron microscope works

Answer 16

Specimen must be thin for electrons to pass through

Electron gun fires electrons

electromagnets focus electrons towards specimen

Fluorescent screen - detects numbers and scattering of electrons and produces an image

Question 17

Advantages of light microscope

Answer 17

Cheaper

Produce coloured images - add stains to specimen

Easy to use

Portable

Question 18

Disadvantages of a light microscope

Answer 18

Lower resolution

Lower magnification

Question 19

Advantages of electron microscope

Answer 19

Higher resolution

Higher magnification

Question 20

Disadvantages of a electron microscope

Answer 20

Expensive

Specimen has to be dead which requires a vaccum

Black and white images

Not portable

Difficult to use

Artefacts can be produced (false images)

Question 21

Transmission electron microscope (TEM)

Answer 21

An electron gun produces and fires electrons which focuses on the specimen by a electromagnet

Beam passes through a thin specimen, part of it absorbs the electrons and the others allow the electrons to pass through, forming a bright image

The resolving power is 0.1nm

Produces a micrograph

Question 22

Disadvantages of a Transmission Electron Microscope (TEM)

Answer 22

Vacum - living organisms cannot be observed

Staining required despite image not being in colour

Specimen must be extremely thin

Image may contain artefacts

Question 23

Scanning Electron Microscope (SEM)

Answer 23

Directs/fires a beam of electrons on to the surface of the specimen rather than penetrating it

Beam passed back and forth in a regular pattern, electrons are scattered by the specimen

Produces a 3D image through computer analysis

Disadvantages are the same as the TEM however the specimen does not need to be thin which is an advantage

The resolving power is 20nm

Question 24

Cell fractionation and Ultracentrifugation - Homogenisation

Answer 24

Homogenisation is the breaking up of cells

The sample must be;

Ice-cold to reduce the activity of enzymes

Isotonic (same water potential as the cells) to prevent water moving into the cells via osmosis

Buffered to prevent enzymes from being degraded

The solution is then homogenised using a homogeniser which is a blender like machine which grinds up the cells

This breaks the plasma membrane of the cells and releases the organelles into a solution called the homogenete

Question 25

Cell fractionation and ultracentrifugation - filtration

Answer 25

The homogenate is filtered to separate out large cell debris

Question 26

Cell fractionation and Ultracentrifugation - Ultracentrifugation

Answer 26

Filtrate placed in a tube and then the tube is placed in a centrifuge. (a centrifuge is a machine that seperates materials by spinning)

The filtrate is first spun at low speed causing heaviest organelles ie nucleus to settle at the bottom as a pellet

The rest of the organelles stay suspended in the solution above (supernatent)

The supernatent is drained off and placed at another tube, which is spun at higher speed

Once again however organelles (mitochondria) settle at bottom forming another supernatent