Cells

Question 1

Eukaryotic cells

Answer 1

Plants- cellulose cell wall
Algae- cellulose cell wall
Animals- no cell walls, cell defines by cell membrane
Protozoan-
Fungi- cell wall made from chitin

Question 2

Nucleus

Answer 2

• Contains DNA
• Largest organelle in the cell.
• Double membrane called the nuclear envelope.
• holes called nuclear pores, allows the passage of molecules such as mRNA, in and out of the nucleus.
• nucleolus, this is where ribosomal RNA is made and ribosomes.
• Ribosomes are made from ribosomal RNA and ribosomal proteins.
• The nucleus also contains chromatin which is made of DNA coiled around proteins called histones. During cell division the chromatin super-condenses and forms chromosomes.

Function:
Contains genetic material
Controls cell activity;

Question 3

Mitochondrion

Answer 3

• Mitochondria are the site of ATP production by aerobic respiration.
• The hydrolysis of ATP releases the energy for cellular/metabolic reactions or provides phosphate for the phosphorylation of molecules to make substances more reactive
• Mitochondria have a double membrane.
• The inner membrane is highly folded to form cristae to increase the surface area for the attachment of ATP synthase enzymes
• Within the inner membrane of the mitochondrion is the matrix which contains proteins, lipids, mitochondrial DNA and ribosomes.
• Cells that need a lot of ATP have lots of mitochondria.

Function:
Site of aerobic respiration;
ATP production

Question 4

Rough Endoplasmic Reticulum

Answer 4

• made from highly folded membranes with 80s ribosomes embedded
• RER synthesises and transports proteins throughout the cell.
• The membrane is folded into flattened sacks called cisternae.
• The RER is joined to the nucleus
• Cells which make lots of protein i.e. secreting extracellular enzymes or antibodies have lots of RER. E.g. enzyme secreting gland cells, or antibodies producing plasma cells.

Function:
Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein within the cell

Question 5

Smooth Endoplasmic Reticulum

Answer 5

• recombines glycerol and fatty acids to make triglycerides.
• The SER packages triglycerides into vesicles and transports them to the golgi apparatus

Function:
Site of lipid synthesis

Question 6

Ribosomes

Answer 6

They are the site of protein synthesis from amino acids.
* Made up of 2 rRNA proteins sub units.
* The eukaryotic cell contains 80s ribosomes.
* two subunits of a ribosome are made of a combination of long strands of rRNA, dotted with ribosomal proteins.

Function:
site of protein synthesis

Question 7

Golgi apparatus

Answer 7

• sorts, modifies and packages molecules, such as proteins and triglycerides into vesicles.
• Golgi vesicles may be used to form lysosomes
• Golgi apparatus is composed of flattened sacs made of membranes.
• Cells which have an extensive Golgi, packages lots of molecules for export commonly large amounts of protein i.e. enzyme secreting gland cells, or antibodies producing plasma cells.
• There is usually only one Golgi body in each cell.

Function:
Modifies/packages/sorts proteins;
Produces vesicles

Question 8

Lysosomes

Answer 8

• hydrolyse damaged and worn out organelles.
• bound by a single membrane and have no internal structure.
• They contain a large number of hydrolytic enzymes, which must be kept separate from rest of cell contents to prevent them from digesting organelles.
• Phagocytes are types of white blood cells that contain many lysosomes, as they breakdown invading pathogens.

Function:
Contains digestive enzymes
Digests worn out organelles

Question 9

Cell Surface Membrane

Answer 9

Made of a Phospholipid Bi-layer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase SA

Question 10

Centrioles

Answer 10

form a network of spindle fibres across the cell onto which the chromosomes attach.
These fibres pull the chromosomes / apart during mitosis.
Not found in plant cells

Question 11

Plants Vs Animals

Answer 11

PLANT CELLS
Cellulose cell wall
Chloroplasts present (not in roots)
Large central vacuole
Carbohydrates stored as STARCH
Has no centrioles

ANIMAL CELLS
No cell wall
No chloroplasts
No large central vacuole
Carbohydrates stored as GLYCOGEN
Has centrioles

Question 12

Chloroplasts

Answer 12

Granum- Stack of thylakoid membranes

Thylakoid membrane- Contains chlorophyll for photosynthesis

Stroma- Fluid filled part, some of the photosynthetic reactions occur here

Starch grains- The energy storage molecule in plants.

DNA and ribosomes- have their own DNA and 70s ribosomes to make enzymes needed for photosynthesis

Function:
- absorbs light energy and converts it to chemical energy, is used to make carbohydrates from CO2 and H2O
- can then be used for respiration

Question 13

Cellulose

Answer 13

• Is very strong, which limits the volume of water that can move into the cell, and stops osmotic lysis
• The wall is permeable to most molecules
• Cell walls of adjacent cells separated by a thin layer called the middle lamella. This acts to stick the walls together with pectin
• has plasmodesmata = gaps in the cell walls that connect cell cytoplasm’s together, allow easy movement of water soluble molecules.

Question 14

What is the function of Capsule

Answer 14

Protects cell from immune systems;
Aids bacteria sticking together;

Question 15

What is the function of Plasmid

Answer 15

Circular DNA;
Contains antibiotic resistance genes;

Question 16

What is the function of Cell Wall

Answer 16

Provides rigid shape
Stops osmotic lysis;

Question 17

What is the function of Flagellum

Answer 17

Allows movement

Question 18

Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.

Answer 18

1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
5. Vesicles transport OR Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane

Question 19

Compare and contrast Eukaryotic and Prokaryotic cells

Answer 19

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
3. DNA in mitochondria similar (structure) to DNA in prokaryotes;

Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Question 20

State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Answer 20

Plant v prokaryote
1. (Associated with) histones v no histones
2. Linear v circular;
3. No plasmids v plasmids;
4. Introns v no introns;
5. Long(er) v short(er);

Question 21

Prokaryotic Vs Eukaryotic

Answer 21

Prokaryotic cell
* DNA is circular and not associated with histones
* Contains no membrane bound organelles.
* Has no ‘true’ nucleus, DNA is free in cytoplasm.
* Contains smaller ribosomes (70s).
* Some have capsule, one or more flagella, one or more plasmids.
* Has mesosomes for ATP synthesis
* Has cell wall made of murein

Eukaryotic cell
* DNA is linear and associated with histones
* Contains membrane bound organelles i.e. mitochondria,
Golgi apparatus,
* Has a nucleus, DNA contained within nuclear membrane.
* Contains larger ribosomes (80s).
* Do not have capsule.
* Does not have mesosomes (has mitochondria)
* Plant cells have a cell wall made of cellulose

Question 22

Light (optical) microscope

Answer 22

• Specimens are illuminated with light
• Specimens can be living or dead
• stained with a coloured dye to make them visible.
• is LIMITED to x1500
• magnification limited - more lenses, loses resolution

Question 23

Name 2 structures found within a eukaryotic cell that cannot be identified using an optical microscope

Answer 23

Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

Question 24

Describe how the student could have used an eyepiece graticule to determine the mean diameter of stomata

Answer 24

1. Measure each stomata using an eye piece graticule
2. Calibrate the eyepiece graticule against a stage micrometer
3. Take at least 5 measurements and calculate a mean (more measurements are more accurate)

Question 25

Give one advantage of using a Transmission Electron Microscope rather than a Scanning Electron Microscope

Answer 25

1. Higher resolution; 2. higher (maximum) magnification / higher detail (of image); OR 2. Allows internal details / structures within (cells) to be seen / cross section to be taken;

Question 26

Give one advantage of using a SEM rather than a TEM.

Answer 26

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

Question 27

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure. Explain the advantages and limitations of using a TEM to investigate cell structure.

Answer 27

Advantages: 1 Small objects can be seen; 2 TEM has high resolution; 3 Electron wavelength is shorter; Limitations: 4 Cannot look at living cells; 5 Must be in a vacuum; 6 Must cut section / thin specimen; 7 Preparation may create artefact;

Question 28

Name 2 structures found within a eukaryotic cell that can be identified using a transmission electron microscope

Answer 28

Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

Question 29

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope.

Answer 29

1. Add a drop of water to the microscope slide; 2. Get a thin section of plant tissue and float on the drop of water; 3. Stain with iodine in potassium iodide 4. Lower the cover slip using a mounted needle to avoid air bubbles;

Question 30

Magnification equation

Answer 30

Actual size = Image size / Magnification 1m = 1000mm. 1 mm = 1000µm 1 µm = 1000nm

Question 31

Cell Fractionation & differential-centrifugation

Answer 31

1) tissue is homogenised in blender in an ice-cold, isotonic, buffered solution * Ice cold: reduce the action of enzymes that would digest organelles. * Isotonic: prevents osmosis of water in or out of organelles, so organelles don’t burst (lyse) or shrivel * Buffered: to stop pH changes which could denature proteins. 2) mixture is then filtered to remove any large pieces of tissue/ cellular debris not broken up by homogeniser producing a solution supernatant 3) Differential centrifugation is carried out on supernatant. It is now centrifuged at high speed . The densest organelles forced to the bottom into a pellet. This pellet is removed. The supernatant can be spun again to obtain the smaller and lighter organelles. 4) The supernatant is now centrifuged at a higher speed for a longer time. The next densest organelles are forced to the bottom into a pellet. This pellet is removed and can be re-suspended if required.