studying cells

Question 1

Describe the structure and function of the nucleus. [6]

Answer 1

Structure
1. Nuclear envelope and pores OR Double membrane and pores;
2. Chromosomes/chromatin OR DNA with histones;
3. Nucleolus/nucleoli;

Function
4. (Holds/stores) genetic information/material for polypeptides (production) OR (Is) code for polypeptides;
5. DNA replication (occurs);
6. Production of mRNA/tRNA OR Transcription (occurs);
7. Production of rRNA/ribosomes;

Question 2

Describe the structure and function of a mitochondrion

Answer 2

Structure
1- double membrane
2- inner membrane fully folded to form Cristae (increase SA )
3- Matrix(liquid part) containing mitochondrial DNA , ribosomes, protein and lipids
Function
1- site of ATP production by aerobic respiration

Question 3

Describe the structure and function of Rough Endoplasmic Reticulum

Answer 3

Structure
1- highly folded membranes with 80s ribosomes embedded
2- the membrane is folded into flattened sacks called Cisternae
3- joined to the nucleus
Function
1- synthesis and transport of protein throughout the cell

Question 4

Describe the structure and function of smooth endoplasmic reticulum

Answer 4

Structure
1- highly folded membranes flattened into sacks called Cisternae
Function
1- recombines glycerol and fatty acids to make triglycerides
2- packages triglycerides into vesicles and transports them to the golgi apparatus

Question 5

Describe the structure and function of cytoplasmic ribosome

Answer 5

Structure
1- made up of subunits that are made of long strands of rRNA and ribosomal proteins

Function
1- site of protein synthesis from amino acids

Question 6

Describe the structure and function of the golgi apparatus/body

Answer 6

Structure
1- flattened sacs made of membranes filled with fluid
2- golgi vesicles pinch off from the main membrane
Function
1- sorts, modifies and packages proteins and triglycerides into vesicles
2- golgi vesicles may be used to form lysosomes

*always involves Proteins

Question 7

Describe the structure and function of lysosomes

Answer 7

membrane-bound oragnelle that stores and releases many hydrolytic enzymes

Question 8

Describe the structure and function of cell surface membrane

Answer 8

Structure
1- made up of phosphplipids, specific transport proteins, and carbohydrates arranged into a Fluid Mosaic Model
Function
1- controls the passage of molecules in and out of the cell

Question 9

Describe the structure and function of centrioles

Answer 9

Structure
- microtubules
Function
1- form a network of spindle fibres onto which chromosomes attach
2- pull chromosomes/chromatids apart during mitosis

*not found in plant cells

Question 10

Describe the structures and functions of Chloroplasts( found in plants and algae)

Answer 10

1- Granum : stack of thylakoid membranes
2- Thylakoid membrane : contains chlorophyll for photosynthesis & ATP synthase enzyme to produce ATP
3- Stroma : fluid filled part, some photosynthetic reactions occur here
4- Starch grains : the energy storage molecule in plants
5- DNA and Ribosomes : contain their own DNA and 70s ribosomes for synthesis of enzymes needed for photosynthesis

Question 11

Describe the structure and function of cellulose cell wall ( in plants and algae)

Answer 11

1- is very strong which limits the volume of water that can move into the cell and stops osmotic lysis ( bursting)
2- the wall is permeable to most molecules
3- has plasmodesmata which are gaps in cell walls that connect cell cytoplasm’s together to allow easy movement of water-soluble molecules

Question 12

what are the cell walls in fungi made of

Answer 12

chitin

Question 13

what are the differences between plant and animal cells

Answer 13

1- cellulose cell wall vs no cell wall
2- chloroplasts present( not in roots) vs no chloroplasts
3- large central vacuole vs no large central vacuole
4- carbohydrates stored as STARCH vs carbohydrates stored as GLYCOGEN
5- has no centrioles vs has centrioles

Question 14

Explain why viruses are described as acellular and non-living. [2]

Answer 14

1- no cell(-surface) membrane OR Not made of cells;
2- (Non-living) have no metabolism/metabolic
reactions;
OR
Cannot (independently) move / respire / replicate / excrete
OR
(Have) no nutrition;

MRSGREN

Question 15

describe the structure and function of a virus

Answer 15

• contain DNA/RNA which can single/double stranded
• surrounded by a protein coat called a capsid
• has attachment proteins which enable it to bind to host cells
• has enzymes that it uses to replicate its genetic information and insert it into the host cell DNA

Question 16

Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. [5]

Answer 16

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; OR Carbohydrate added/glycoprotein produced by Golgi apparatus;
5- Vesicles transport OR Rough endoplasmic reticulum transports;
6- (Vesicles) fuse with cell(-surface) membrane;

Question 17

Compare & contrast Eukaryotic and Prokaryotic DNA [5]

Answer 17

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / 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 18

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

Answer 18

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

Question 19

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different

Answer 19

1- Cholera bacterium is prokaryote;
2- Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;

3 and 4 Any two from: [No membrane-bound organelles/no mitochondria / no golgi/no endoplasmic reticulum];
5- Small ribosomes only;
6- and 7 Any two from [Capsule/flagellum/plasmid / cell wall]

Question 20

Name two structures found in all bacteria that are not found in plant cells.

Answer 20

1- Circular DNA (molecule in cytoplasm);
2- Murein cell wall OR Peptidoglycan cell wall OR Glycoprotein cell wall;
3- Small(er)/70S ribosomes (in cytoplasm);

Question 21

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

Answer 21

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

Question 22

The resolution of an image obtained using an electron microscope is higher than the resolution of an image obtained using an optical microscope. Explain why.

Answer 22

Shorter wavelength between electrons

OR

Longer wavelength in light (rays);

Question 23

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

Answer 23

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

Question 24

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. [6]

Answer 24

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 25

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:
a) Isotonic
b) Ice cold
c) buffered

Answer 25

a) ISOTONIC: Prevents osmosis / no (net) movement of water So organelle/named organelle does not burst/shrivel;
b) ICE COLD: Reduce/prevent enzyme activity so organelles are not digested / damaged;
c) BUFFERED: Maintain a constant pH so proteins do not denature;

Question 26

Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells. [6]

Answer 26

1- Cell homogenisation to break open cells and release organelles;
2- Filter to remove (large) debris/whole cells;
3- Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
4- Keep cold to prevent/reduce damage to organelles by enzyme;
5- Use buffer to maintain pH and prevent protein/enzyme denaturation;
6- Use differential Centrifuge (at high speed/1000 g) to separate nuclei / cell fragments / heavy organelles;
7- Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
8- Observe pellet with a microscope to identify mitochondria;

Question 27

Compare prokaryotic cells with eukaryotic cells

Answer 27

1- Circular DNA associated with histones vs Linear DNA not associated with histones
2- contains no membrane bound organelles vs does contain membrane bound organelles
3- has no true nucleus, DNA is free in nucleus vs has a nucleus,DNA contained within nuclear membrane
4- contains smaller 70s ribosomes vs contains larger 80s ribosomes
5- some have capsule,one or more flagella/plasmids vs do not have capsule.
6- has mesosomes for ATP synthesis vs has mitochondria instead
7- has cell wall made of murein or peptidoglycan vs plant cells have a cell wall amde of cellulose

Question 28

Describe how u 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 microscope

Answer 28

1- add a drop of water to the microscope slide
2- get a thin section of plant tisuue and float on the drop of water
3- stain with KI solution
4- lower the cover slip using a mounted needle to avoid air bubbles