Cell Structure

Question 1

Structure of nucleus

Answer 1

Largest organelle (10-20um in diameter). Roughly spherical. Surrounded by the nuclear envelope (double membrane) containing nuclear pores (openings). Outer membrane joins to endoplasmic reticulum. Nucleoplasm contains chromatin (DNA and histones seen as dark blobs or fibre)

Question 2

Function of nucleus

Answer 2

Contains genetic material and instructions for making protein. Controls protein synthesis (bases and nucleotides) and makes mRNA

Question 3

Structure of nucleolus

Answer 3

Not surrounded by a membrane. Sense spherical structure inside nucleus.

Question 4

Function of nucleolus

Answer 4

Makes RNA and ribosomes. Pass into the cytoplasm through nuclear pores

Question 5

Stages of preparing cells for electron microscopes

Answer 5

Homogenisation, filtration and ultracentrifugation

Question 6

Homogenisation

Answer 6

Cell breaks open by being grinder down or vibrated. Cold, isotonic buffer added. Cold: slows down organelle activity esp hydrolytic enzymes in lysosomes. Isotonic: prevent movement of water into and out of the cell via osmosis so water potential remains the same. Buffer solution: maintain pH so there will be no denaturation of proteins

Question 7

Filtration on cell preparation for microscopes

Answer 7

Filtered through a gauze to get rid of cell debris

Question 8

Ultracentrifugation

Answer 8

Spun slowly so heavier organelles go to the bottom and lighter ones suspend above (supernatant). Spin again faster so mitochondria and lysosomes are at the bottom in the pellet. Drain supernatant off and spin again even faster so lightest organelles remain

Question 9

What is mitosis?

Answer 9

Cell division of somatic cells to produce two diploid daughter cells that are genetically similar to each other and the parent cell

Question 10

What is meiosis?

Answer 10

Division of cells to produce four haploid daughter cells that are genetically different to each other and the parent cell

Question 11

How do prokaryotic cells divide?

Answer 11

Binary fission. Circular DNA replicates and attach to cell membrane. Plasmids replicate. Cell membrane grows between the DNA molecules and pinches inward to divide the cytoplasm in two. New cell wall forms to give two genetically identical daughter cells with one copy of circular DNA and variable number of plasmid copies

Question 12

How do viruses replicate?

Answer 12

Non-living so do not undergo cell division. Go through lytic or lysogenic cycles where they inject their nuclei acid in a host cell by attaching to it on proteins on the surface. Host’s metabolic processes produce viral components to make viruses

Question 13

Cytokinesis in plants

Answer 13

No centrioles but spindle fibres remain. New cell wall is developed: vesicles from Golgi body collect at the equator, fuse together to form a cell plate, cellulose builds up to form cell wall, plasma membrane on both sides

Question 14

Cytokinesis in animals

Answer 14

Centrioles at each pole, spindle fibres degenerate at telophase, cell membrane invaginates in at the equator forming a cleavage furrow, cell membrane meets in the centre to form two separate cells

Question 15

Retrovirus def

Answer 15

Attack RNA of a cell

Question 16

Apoptosis def

Answer 16

Programmed cell death

Question 17

What are the two subunits of ribosomes?

Answer 17

80S in eukaryotic cells, 25nm in diameter; and 70S in prokaryotic cells, mitochondria and chloroplasts

Question 18

Structure of ribosome

Answer 18

One large and one small subunit (ribosomal RNA and protein). Small cytoplasmic granules. Occur in the cytoplasm or are associated with RER

Question 19

Function of ribosomes

Answer 19

Site of protein synthesis - translation stage

Question 20

Structure of RER (rough endoplasmic reticulum)

Answer 20

Ribosomes present themselves on the outer surfaces of the membranes. (More linear than SER)

Question 21

Nuclear envelope structure and function

Answer 21

Double membrane that surrounds the nucleus. The outer membrane is continuous with the endoplasmic reticulum and has ribosomes on the surface. It controls the entry and exit of materials in and out the. Uncle us and contains the reactions taking place within it

Question 22

Nuclear pores structure and function

Answer 22

Gaps in the outer surface of the nucleus, each 50-100 nm in diameter. There are typically 3000 pores in each nucleus. Allows the passage of large molecules out the nucleus eg mRNA

Question 23

Nucleoplasm structure and function

Answer 23

Granular, jelly-like material that makes up the bulk of the nucleus

Question 24

Cisternae structure and function

Answer 24

Sacs formed by the double membranes of smooth and rough ER. Synthesise and collect protein molecules in the cisternal lumen

Question 25

Function of rough endoplasmic reticulum

Answer 25

Provides a large surface area for the synthesis of proteins and glycoproteins. Provides a pathway for the transport of materials e.g. proteins throughout the cell

Question 26

Structure of SER (smooth endoplasmic reticulum)

Answer 26

Lacks ribosomes on the surface and is more tubular in appearance. (More tangled than RER)

Question 27

Function of smooth endoplasmic reticulum

Answer 27

Synthesises, stores and transports lipids and carbohydrates

Question 28

Structure of Golgi apparatus

Answer 28

Compact. Consists of cisternae with vesicles (small rounded hollow structures)

Question 29

Function of Golgi apparatus

Answer 29

Adds carbohydrates to proteins to form glycoproteins. Produces secretory enzymes e.g. from the pancreas. Secrete carbohydrates e.g. those used in making cell walls in plants

Question 30

Structure of mitochondria

Answer 30

Usually rod-shaped. 1-10um in length. Has a double membrane around it to control the entry and exit of material. Inner of these two membranes food to form cristae, which are extensions that provide a large surface area for the attachment of proteins and enzymes. The matrix makes up the remainder, containing protein (including enzymes), lipids, ribosomes and DNA to control protein production

Question 31

Function of mitochondria

Answer 31

Site of aerobic respiration (Krebs cycle and oxidative phosphorylation). Produces ATP

Question 32

Structure of chloroplasts

Answer 32

Disc-shaped. 2-10 um long. 1um in diameter. Have a chloroplast envelope with a double plasma membrane surrounding it and controls what goes in and out. Have grana which are stacks of thylakoids that have chlorophyll; it’s where the first stage of photosynthesis takes place

Question 33

Structure of lysosomes

Answer 33

1um in diameter. Formed when vesicles contain enzymes, such as lysozymes, proteases and lipases. Up to 50 enzymes in every lysosome

Question 34

Function of lysosomes

Answer 34

Hydrolyse material engulfed by phagocytes. Release enzymes by exocytosis to destroy material around the cell. Destroy worn out organelles. Break down dead cells after apoptosis (autolysis)

Question 35

Structure of the cell wall

Answer 35

Consist of microfibrils of cellulose in a matrix to give strength. Has a thin layer called the middle lamella which cements adjacent cells together

Question 36

Function of cell walls

Answer 36

Provides mechanical strength to prevent cell lysis (bursting) under pressure from osmosis. Strengthens the plant. Allows water to pass along it

Question 37

Cell walls of plants vs algae vs fungi

Answer 37

Plants: cellulose, algae: either cellulose, glycoproteins or a mix of both, fungi: chitin (nitrogen-containing polysaccharide), glycan and glycoproteins

Question 38

Structure of the vacuoles

Answer 38

A fluid filled sac founded by single membrane called a tonoplast. Contain a selection of mineral salts, sugars, amino acids, wastes and sometimes pigments eg anthocyanins

Question 39

Function of vacuoles

Answer 39

Support herbaceous plants by making cells turgid. Sugars and amino acids act as temporary food store. Pigments colour petals to attract pollinating insects

Question 40

Compare light microscopes and transmission electron microscopes

Answer 40

TEM shows no colour, light microscopes do. TEMs use magnets to focus, light microscopes use glass lenses. TEMs uses dead specimens, light microscopes use living specimens. TEMs have greater resolution. Light microscopes use visible light whereas TEMs use beams of electrons. TEMs have higher resolving power. TEMs have a longer preparation stage that’s more complicated.

Question 41

Function of protein channels

Answer 41

Controls what goes in and out of the plasma membrane by facilitated diffusion to maintain ion concentration. Water soluble ions diffused across the membrane

Question 42

Why are phospholipids orientated in a particular way?

Answer 42

Hydrophilic heads are attracted to the water environment and therefore on the outside. Whereas hydrophobic tails repel away from the water environment and all therefore on the inside.

Question 43

What is the pH of blood?

Answer 43

4

Question 44

How do sodium ions that are pumped out of the epithelial cells into the bloodstream help glucose be absorbed from the lumen of the ileum?

Answer 44

The concentration of sodium ions in the cells is less than the concentration in the lumen. Sodium ions diffuse into the cell down the concentration gradient. Glucose moves in with sodium ions via co-transport proteins