B2- Scaling Up

Question 1

What are the parts of the cell cycle and what happens in during those phases?

Answer 1

G1- Gap Phase 1: cell grows and new cell structures and proteins are made. Cell contents are duplicated.

S phase- Synthesis: cell replicates its DNA so that when it splits during mitosis the two new cells will contain identical DNA.

G2- Gap Phase 2: cell keeps growing and proteins needed for cell division are made. Cell checks for errors in DNA and makes spindle fibres.

M- Mitosis: the cycle starts and ends here, when the cell reproduces itself by splitting to form two identical daughter cells.

Question 2

What is mitosis?

Answer 2

Cell division in all somatic cells (except in testes and ovaries). Takes 16-24 hours for mitosis to happen.
300,000 new cells a day!

Question 3

What is meosis?

Answer 3

Takes place in ovaries and testes.
Makes gametes (sex cells).
Germline- germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny (offspring).

Question 4

What happens during mitosis?

Answer 4

1) Chromosomes become visible in the nucleus after undergoing DNA replication
2) Chromosomes shorten and appear as chromatids joined by a centromere.
3) The nuclear membrane disappears and the chromosomes line up at the cell’s equator.
4) Centrioles migrate towards opposite cellular poles.
5) Chromatids are pulled apart to opposite poles by contracting spindle fibres.
6) The nuclear membrane forms around each group of chromatids and the cytoplasm divides.
7) 2 new daughter cells are formed. They are identical.

Question 5

What is differentiation?

Answer 5

Differentiation is the process by which a cell changes to become specialised for its function.
Plant cells never lose this ability, but most animal cells do.

Question 6

What are stem cells?

Answer 6

Stem cells are differentiated. Depending on what instructions they’re given, they can divide by mitosis to become new cells, which then differentiate.

Question 7

What are embryonic stem cells?

Answer 7

Embryonic stem cells are found in early human embryos. They have the potential to turn into any kind of cell at all.
This means that stem cells are really important for growth and development of organisms.
Come from Blastocysts (3-5 days old)
No rejection from body.
Disadvantage: we cant get them once we are older and the only other way to get them is from Embryos from IVF which is argued to be unethical.

Question 8

What are adult stem cells?

Answer 8

Adult stem cells are only found in a few places, like red bone marrow.
They aren’t as versatile as embryonic stem cells- they can’t turn into any cells type at all, differentiate into any blood cell only.
They are used to replace damaged cells.

If it is not your ASC, there is a chance of rejection.

Question 9

What are meristems?

Answer 9

Meristems are plant stem cells.
They are found in the plant tissues and are the only cells that divide by mitosis.
Meristem tissue is found in the areas of a plant that are growing- such as the roots and shoots.
Meristems produce unspecialised cells that are able to divide and form any cell type in the plant- they act like an ESC.
These cells can divide to generate any type of cell for as long as the plant lives.

Question 10

What is diffusion?

Answer 10

Diffusion is the net overall movement of particles from an area of higher concentration to an area of lower concentration down a diffusion gradient.
Until an equilibrium is reached- even then the particles do not stop moving.
It occurs in both liquids and gases- the particles in these states are free to move randomly.

Question 11

What is Active transport?

Answer 11

Active transport is the movement of particles across a partially permeable membrane against a concentration gradient- from an area of lower concn to an area of higher concn using ATP released during respiration.

Active Transport allows nutrients to be taken into the blood despite the fact that the concn gradient is the wrong way.

Question 12

What is Osmosis?

Answer 12

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential via a partially permeable membrane down a water potential gradient.

Pure water has the highest water potential.

Question 13

What factors affect the rate of diffusion?

Answer 13

Temperature: more kinetic energy
Concn: high concn to low concn faster than two similar concn.
Distance: it would take a molecule of O2 4 hours to travel a distance of 1cm.

Question 14

Why does watering a plant help it stay upright? What happens when there is no water in the soil?

Answer 14

• Watering a plant increases the water potential of the soil around it.
• This means all of the plant cells draw water in by osmosis until they become turgid (plump and swollen)
• Contents of cell push against the cell wall- this is called turgor pressure.
• Turgor pressure helps support the plant tissues
• If there is no water in soil, a plant starts to wilt.
• Cell is plasmolysed (cytoplasm pulls away from cell wall).
• This is because the cell become flaccid (start to lose water)
• The plant does not lose its shape through, as the inelastic cell wall keep things in position.

Question 15

What does: hypertonic, isotonic and hypotonic mean?

Answer 15

Hypertonic: Hypertonic means that the environment outside of the cell has a higher water potential than the cell itself. That will attract water molecules from the cell leading to the shrinking of the cell.

Isotonic: the solutions on either side of a cell membrane are isotonic if the water potential outside the cell is equal to the water potential inside the cell.

Hypotonic: a solution outside of a cell is called hypotonic if it has a lower concentration of solutes relative to the cytosol. Due to osmotic pressure, water diffuses into the cell, and the cell often appears turgid, or bloated.

Question 16

What is the process of haemolysis?

Answer 16

Haemolysis is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma).

Question 17

What does crenated mean?

Answer 17

Crenation describes the formation of abnormal notched surfaces on cells as a result of water loss through osmosis. The cells start to shrivel and form abnormal spikes and notches on the cell membrane.

Question 18

What does osmoregulation mean?

Answer 18

Osmoregulation is the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations.

Question 19

Why do animal cells burst with a hypertonic solution but plant cells do not?

Answer 19

Plant Cells have a cell wall which is made of cellulose, so it is strong and does not burst easily.
Animal cells do not have a cell wall, so the membrane can burst easily with a hypertonic solution.

Question 20

What is the formula for percentage change in mass?

Answer 20

Percentage change = final mass - initial mass
——————————– x 100
initial mass

Question 21

What are the main factors that affect the movement of substances?

Answer 21

• Surface Area to Volume Ratio: The rate of diffusion, osmosis and active transport is higher in cells with a larger surface area to volume ratio.
• Temperature: As particles in the substance get warmer they have more energy, so they move faster. This means as temperature increases, substances move in and out of cells faster.
• Concentration Gradient: Substances move in + out of cell faster if there is a big difference in concentration between the inside and outside of the cell. If there are lots more particles on one side, there are more there to move across.

Question 22

What is urea?

Answer 22

Urea is produced as a waste product from the reactions. Urea is poisonous so it needs to be removed from the body. it is filtered out of the blood by the kidneys and removed from the body in the urine.

Question 23

Describe the differences of how single-cellular organisms exchange surfaces in comparison to multicellular organisms:

Answer 23

Single-celled organisms exchange substances differently to multicellular organisms.
As they are only 1 cell big, substances can diffuse straight into and out of them across the membrane. Diffusion is quite quick because:

• Substances only have to travel a short distance
• Single-celled organisms have a relatively large SA:VR this mean they are able to exchange enough substances across their cell membrane to supply the volume of the cell

In multi-cellular organisms, it is more difficult to exchange substances, diffusion across the outer membrane is too slow because:

• Some cells are deep inside the organism, it is a long way from them to the outside environment,
• Larger organisms have a low SA:VR so it is difficult to exchange enough substances to supply a large volume of organism through a relatively small outer surface.

So, instead of exchanging substances through their outer membrane, multicellular organisms need specialised exchange organs, each with a specialised exchange surface.

They also need transport systems to carry materials from the exchange organs to the body cells and to remove waste products.
In animals, the transport system is the circulatory system.
In plants, its the xylem and phloem vessels.

Question 24

How are the exchange surfaces in the human body adapted to maximise exchange?

Answer 24

The exchange surfaces in specialised exchange organs are adapted to maximise effectiveness:

• They are thin, so substances have a short distance to travel
• They have a large surface area, so lots of a substance can move at once
• Exchange surfaces in animals have lots of blood vessels to get stuff into and out of the blood quickly.
• Gas exchange surfaces (alveoli) are often ventilated too, air moves in and out.

Question 25

Explain how gas exchange occurs in our lungs:

Answer 25

• The function of our lungs is to transfer oxygen to the blood and to remove waste CO2 from it.
• To do this the lungs contain millions of air sacs called alveoli where gas exchange takes place.
• The alveoli are specialised to maximise the diffusion of oxygen as they have:
• Enormous SA (75m^2 in humans)
• very thin walls
• a moist lining for dissolving gases
• a good blood supply.

The blood passing next to the alveoli has just returned to the lungs from the rest of the body via the heart, so it contains lots of CO2 and very little oxygen.

CO2 diffuses out of the blood (higher concn) into the alveolus (lower concn) to be breathed out.

Oxygen diffuses out of the alveolus (higher concn) into the blood (lower concn).

Question 26

What are villi and how are they adapted to be an effective exchange surface?

Answer 26

-The small intestine is where dissolved food molecules are absorbed out of the digestive system and into the blood.
-The inside of the small intestine is covered in millions of villi.
-They increase the SA so that the dissolved food molecules are absorbed much more quickly into the blood.
They have:
-a single later of surface cells
-a very good blood supply to assist quick absorption.

Question 27

How are leaves specialised to maximise the diffusion of O2 and CO2?

Answer 27

• Leaves are broad, so there’s a large SA for diffusion.
• They’re also think, which means gases only have to travel a short distance
• There are air spaces inside the leaf. This lets gases like CO2 and O2 move easily between cells. It also increases the SA for gas exchange.
• The lower surface is full of little holes called stomata. They’re there to let gases like CO2 diffuse in and out. they also allow water to escape- which is known as transpiration.

Question 28

How are root hairs adapted to maximise exchanging water and mineral ions?

Answer 28

• The cells on plant roots grow into long ‘hairs’ which stick out into the soil.
• each branch of a root will be covered in millions of these microscopic hairs.
• This gives the plant a big surface area for absorbing water and mineral ions from the soil.
• There is usually a higher concentration of water in the soil than there is inside the plant, so the water is drawn into the root hair cell by osmosis.
• Mineral ions move in by active transport, since the concentration of mineral ions in the root hair cells is usually higher than in the soil.

Question 29

What are the advantages of having a double circulatory system?

Answer 29

• Advantages of double circulatory system include:
• Returning the blood to the heart after it’s picked up oxygen at the lungs means it can be pumped out around the body at a much higher pressure
• This increases the rate of blood flow to the tissues (blood can be pumped around the body much faster) so more oxygen can be delivered to the cells.
• This is important for mammals because they use up a lot of oxygen maintaining their body temperature.
• blood goes through heart twice
• 1st organ to get fresh oxygenated blood is the heart

Question 30

Why is the left ventricle of the heart thicker than the right?

Answer 30

The left ventricle of the heart is thicker than the right because blood from the left ventricle has to travel around the body under high pressure. Blood from the right valve only goes to the lungs.

Question 31

What is the function of the semi-lunar valve/bicuspid/tricuspid valve?

Answer 31

To ensure blood flows in ONE DIRECTION and no BACKFLOW.

Question 32

Why do mammals need a double circulation system?

Answer 32

Mammals are very active animals- need a double circulation system:

• blood pressure is higher especially to the body tissues, so blood is pumped faster than with a single circulation.
• there is a higher blood flow to the body tissues. This means that more oxygen can be carried to the body cells for respiration to supply the energy needed and waste products can be removed quickly.
• oxygenated blood is separate from deoxygenated blood.

Question 33

Describe the adaptations of the blood vessels that withstand the internal conditions of a double circulation system:

Answer 33

The thick elastic walls of arteries withstand the high pressure of the blood.
Capillary networks have a large exchange surface area.
The think permeable walls of capillaries mean that substances have only a short distance to diffuse.
Large lumen in the veins gives the least flow resistance.
Valves in the veins prevent the backflow of blood.

Question 34

Describe the disadvantages of a single circulatory system?

Answer 34

• blood goes through the heart once
• last organ to get oxygenated blood is the heart
• deoxygenated blood and oxygenated blood are not separated.
• low pressure.