Topic 1 Cell Biology 1.4-1.6

Question 1

1.4 What is endocytosis?

Answer 1

Process of capturing a substance or particle from outside of the cell by engulfing it with the cell membrane- forms vesicles that contains materials from outside of cell.

Question 2

1.4 Example of endocytosis

Answer 2

Specialised white blood cells engulfing invading microorganisms to defend the body against infection, and remove cell debris by ingesting damaged/ old cells.

Question 3

1.4 What is exocytosis?

Answer 3

Process of vesicles fusing with the plasma membrane to release their contents to the outside of cell.

Question 4

1.4 Example of exocytosis

Answer 4

Pancreas secreting the hormones glucagon and insulin to regulate glucose levels throughout the body.

Question 5

1.4 What is simple diffusion?

3 points

Answer 5

• Process where a substance passes through a membrane without the aid of intermediary eg. integral protein.
• From an area of higher concentration to an area of lower concentration- along the concentration gradient.
• It is a passive process.

Question 6

1.4 Example of simple diffusion

Answer 6

Diffusion of oxygen through phospholipid bilayers. Occurs when it is more concentrated in alveolar air space than blood circulating around lungs.

Question 7

1.4 What is facilitated diffusion?

Answer 7

Process where a substance that cant diffuse between phospholipids passes through a membrane using channels- helping particles pass through.

Question 8

1.4 How do cells control the substances that diffuse in and out through channels?

Answer 8

Diameter and chemical properties of channel proteins determine the type of particle that passes through it.
Cells can control which types of channels are placed in the plasma membrane.

Question 9

1.4 What is active transport?

3 points

Answer 9

• Process where cells take in substances even though there is already a higher concentration inside. OR pumping out substances even though there is a higher concentration outside.
• Moves against the concentration gradient
• Not diffusion, requires ATP

Question 10

1.4 What proteins carry out active transport?

Answer 10

Globular proteins/ pump proteins

Question 11

1.4 Example of active transport

Answer 11

Axons in neurons (nerve cell), sodium-potassium pump follows a cycle, each cycle uses one ATP.

1) Pump open to inside of axon, 3 sodium ions attach to binding sites
2) Phosphate from ATP attaches to pump, changing its shape
3) Pump opens to outside of axon, releasing sodium ions.
4) 2 potassium ions attach binding sites
5) Binding of potassium releases phosphate, changing pump shape again
6) Potassium ions are released, cycle can repeat.

Question 12

1.4 What is osmosis?

Answer 12

The net movement of water going from a region with lower solute concentration to one of higher concentration. Passive process.

Question 13

1.4 Why does water move from a region of lower solute concentration to one of higher concentration? (in regard to water molecules)

Answer 13

Higher solute concentration = less water molecules that are free to move because substances dissolve by forming intermolecular bonds, restricting the movement of water molecules. So it moves from an area with more water molecules to less- like diffusion and its concentration gradient.

Question 14

1.4 Example of osmosis

Answer 14

Kidney cells reabsorbing water (Kidney- regulates water and ion balance of the blood plasma, keeping the level of urea low)

1) Small molecules including water and glucose are filtered from blood
2) Kidneys reabsorbs the molecules which are needed, molecules that are not needed will be excreted as urine
3) Absorbing as much water as the body needs to maintain a constant water level in the blood plasma is done through osmosis!

Question 15

1.4 What are hypertonic solutions and what are its effect on cells.

Answer 15

Hypertonic = solution with higher osmolarity, high solute concentration
Water leaves cells by osmosis (water concentration lower outside of cell), cytoplasm shrinking in volume but area does not change, cells will lose mass.

Question 16

1.4 What are hypotonic solutions and what are its effect on cells.

Answer 16

Hypotonic= solution with lower osmolarity, low solute concentration.
Water enters cells by osmosis (water concentration higher outside of cell), cell swells up and may burst, strong cellulose walls can prevent this.

Question 17

1.5 Name the possible sequence of first cells from non-living material.

Answer 17

1) Production of carbon compounds (such as sugars and amino acids)
2) Assembly of carbon compounds into polymers
3) Formation of membranes
4) Development of a mechanism for inheritance

Question 18

1.5 Describe the ‘production of carbon compounds’

Answer 18

Stanley Miller and Harold Urey passed steam through a mixture of ammonia, methane and hydrogen to simulate the early atmosphere with electric discharges to simulate lightning. Found that carbon compounds were produced.

Question 19

1.5 Describe the ‘assembly of carbon compounds into polymers’

Answer 19

Deep sea vents gushes out inorganic chemicals that represents the supply of energy to form polymers from carbon compounds

Question 20

1.5 Describe the ‘formation of membranes’

Answer 20

Phospholipids/ other amphipathic compounds would naturally form bilayers, where they readily form vesicles, which resembles the membrane of a small cell. This allows different internal chemistries to develop.

Question 21

1.5 Describe the ‘development of a mechanism for inheritance’

Answer 21

When RNA was the genetic material- it stores information like DNA, self-replicates and acts as a catalyst.

Question 22

1.5 What is the endosymbiotic theory?

Answer 22

Theory that mitochondria and chloroplasts in eukaryotes were once free living prokaryotes that were took in by larger prokaryotes through endocytosis.

Question 23

1.5 What is a symbiotic relationship in relation to endosymbiotic theory?

Answer 23

Smaller aerobically respiring/ photosynthesising cells (mitochondria and chloroplasts) carries out respiration/ photosynthesis and supply energy to larger cell while larger cell provides it with food and a stable environment to live in.

Question 24

1.5 What are the evidence that supports the endosymbiotic theory?

Answer 24

• Have their own genes on a circular DNA molecule like that of prokaryotes
• Have ribosomes that are the same size and shape
• Synthesises their own proteins
• Only produced by division of pre-existing mitochondria/ chloroplasts

Question 25

1.5 What was pasteur’s experiment?

Answer 25

Prepared nutrient broth in long necked flasks, one straight (broken) and one bent, both flasks are sterilised by boiling. Both sat in room temp and are exposed to air. Over time dust particles started to collect in broth of straight neck flask, turning it cloudy (sign that it teemed with microbial life), while dust particles collected in the neck of the curved neck flask.

Question 26

1.5 What were the conclusions of pasteur’s experiment?

Answer 26

There is no spontaneous generation as life only arose with the introduction of dust on which the microbes can travel on. Therefore, germs could only come from other germs.

Question 27

1.6 What is mitosis and what is it needed for?

Answer 27

Division of the nucleus into two genetically identical daughter nuclei. Needed for embryonic development, growth, tissue repair, asexual reproduction.

Question 28

1.6 What are the stages of mitosis and what comes before and after it?

Answer 28

PMAT- prophase, metaphase, anaphase and telophase.
Before- interphase
After- cytokinesis

Question 29

1.6 What happens in interphase?

Answer 29

Active phase of cell cycle, DNA replicates in nucleus and protein synthesis in cytoplasm, mitochondria increase.
Split into 3 stages
G1- cellular contents, excluding chromosomes are duplicated
S- each of the 46 chromosomes is duplicated by the cell
G2- cell double checks duplicated chromosomes for error, making any needed repairs