Chapter 3 Cells

Question 1

What are the properties of light microscopes?

Answer 1

-Beam of light is condensed to create the image.
-Poorer resolution due to light having a longer wavelength.
-Lower magnification
-Colour images
-Can view living samples.

Question 2

What are the properties of electron microscopes?

Answer 2

-Beam of electrons is condensed, using an electromagnet, to create the image.
-Higher resolving power as the electrons have a shorted wavelength.
-Higher magnification
-Black and white images.
-Sample must be in vaccum, therefore non-living.

Question 3

Why must samples be in a vacuum for an electron microscope?

Answer 3

As electrons are absorbed by air.

Question 4

How does a transmission electron microscope work?

Answer 4

Extremely thin specimens are stained and placed in vacuum. Electron gun produces beam of electrons that pass through specimen. Some parts absorb electrons and appear dark..

Question 5

How does a scanning electron microscope work?

Answer 5

Specimens do not need to be as thin. Electrons are beamed onto the surface and electrons are scattered in different ways depending on contours. Produces 3D image.

Question 6

How do you convert from mm to micrometre?

Answer 6

X 1000

Question 7

Why should cells be prepared in a cold solution?

Answer 7

To reduce enzyme activity. When cell is broken open enzymes are released which could damage the organelles.

Question 8

Why should cells be prepared in an isotonic solution?

Answer 8

To prevent osmosis, as this could cause the organelles to shrivel or burst.

Question 9

Why should cells be prepared in buffered solution?

Answer 9

To prevent damage to organelles.

Question 10

What happens in homogenisation?

Answer 10

Cells must be broken open and this is done using a blender. Cells are blended in cold, isotonic and buffered solution.
The solution is filtered to remove the large cell debris.

Question 11

What happens in ultracentrifugation?

Answer 11

-Centrifuge spins at high speeds and centrifugal forces cause pellets of most dense organelle to move to bottom of tube.
-Process is repeated at increasingly faster speeds removing supernatant each time, leaving behind the pellet.

Question 12

What is the order of organelle fractionation?

Answer 12

Nuclei
Chloroplasts
Mitochondria
Lysosomes
Endoplasmic Reticulum
Ribosomes

Question 13

Structure of nucleus

Answer 13

Nuclear envelope- Double membrane
Nuclear pores- allows mRNA to come out of nucleus.
Nucleoplasm - Granular jelly-like material
Chromosomes- protein bound, linear DNA.
Nucleolus- Small sphere inside inside which is site of rRNA production and makes ribosomes.

Question 14

Function of Nucleus

Answer 14

Site of DNA replication and transcription (making mRNA)
Contains genetic code for each cell.

Question 15

Structure of Endoplasmic reticulum.

Answer 15

Both smooth and rough have folded membranes called cisternae.
Rough have ribosomes on cisternae.

Question 16

Function of RER

Answer 16

Protein synthesis

Question 17

Function of SER

Answer 17

Synthesis and store lipids and carbohydrates.

Question 18

Structure of Golgi Apparatus & Vesicles

Answer 18

Folded membranes making cisternae
Secretary vesicles pinching off from the cisternae.

Question 19

Function of Golgi Apparatus

Answer 19

Add carbohydrates of proteins to form glycoproteins.
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids.
Form lysosomes
Molecules labelled to indicate their destination.
Finished products are transported to cell surface in golgi vesicles where they fuse with the membrane and the contents in released.

Question 20

Structure of lysosomes

Answer 20

Bags or vesicles of digested enzymes- can contain 50 different enzymes.

Question 21

Function of lysosomes

Answer 21

Hydrolyse phagocytic cells
Completely break down dead cells (autolysis)
Exocytosis- release enzymes to outside of cell to destroy material
Digest worn out organelles for reuse of materials.

Question 22

Structure of mitochondria

Answer 22

Double membrane
Inner membrane called the cristae
Fluid centre called mitochondrial matrix
Loop of mitochondrial DNA

Question 23

Function of mitochondria

Answer 23

Site of aerobic respiration
Site of ATP production
DNA to code for enzymes needed in respiration

Question 24

Structure of ribosomes

Answer 24

Small, made up of two sub units of protein and rRNA.
80s- large ribosome found in eukaryotic cells
70s- smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.

Question 25

Function of ribosomes

Answer 25

Site of protein synthesis.

Question 26

Structure of vacuole

Answer 26

Filled with fluid surrounded by a single membrane called a tonoplast.

Question 27

Function of vacuole

Answer 27

Make cells turgid and therefore provide support
Temporary store sugars and amino acids
The pigments may colour petals to attract pollinators.

Question 28

Structure of chloroplasts

Answer 28

Surrounded by double membrane
Contains thylakoids (folded membranes embedded with pigment).
Fluid filled stroma contains enzymes for photosynthesis.
Found in plants

Question 29

Function of chloroplast

Answer 29

The site of photosynthesis.

Question 30

Structure of cell wall

Answer 30

Found in plant and fungi cells
Plants- made of microfibrils of the cellulose polymer
Fungi- made of chitin, a nitrogen containing polysaccharide.

Question 31

Function of cell wall

Answer 31

Provide structural strength to cell.

Question 32

Structure of plasma membrane.

Answer 32

Found on outside of all cell
Phospholipid bilayer- molecules embed within and attached on outside (proteins, carbohydrates & cholesterol.

Question 33

Function of plasma membrane

Answer 33

Controls entrance and exit of molecules.

Question 34

What happens in prophase?

Answer 34

-Chromosomes condense and become visible.
-In animal cells, centrioles separate and move to opposite poles of cell.
-Nuclear envelope starts to break down.

Question 35

What happens in metaphase?

Answer 35

-Chromosomes align along equator of cell.
-Spindle fibres released from poles, now attach to centromere and chromatid.

Question 36

What happens in anaphase?

Answer 36

-Spindle fibres retract and pull centromere and chromatids they are bound to towards opposite poles.
-This causes centromere to divide into two and chromatids pulled to opposite poles.
-These separated chromatids now referred to as chromosomes.
-This stage requires energy in form of ATP in the mitchondria.

Question 37

What happens in telophase?

Answer 37

-Chromosomes are now at each pole of cell and become longer and thinner again.
-Spindle fibres disintegrate and nucleus starts to reform.
-The final stage in cell cycle is when cytoplasm splits in two to create the two new genetically identical cell.

Question 38

What is the cell wall made of in prokaryotic cells?

Answer 38

Murein

Question 39

What type of ribosomes are found in prokaryotic cells?

Answer 39

70S

Question 40

How do prokaryotic cells keep their DNA?

Answer 40

In a single circular DNA molecule free in the cytoplasm which is not protein bound.
In plasmids which are small loops of DNA which only carry a few genes.

Question 41

What is the capsule and what does it do?

Answer 41

The capsule is a slimy layer made of protein. This prevents the bacteria from desiccating (drying out) and protects bacteria against the host’s immune system.