Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OCR Biology A level > Exchange and Transport > Flashcards

Exchange and Transport Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

7.1
How do most substances leave or enter organisms?

A

Most substances - gases, nutrients, ions, etc. - cross cells surface membranes to enter or leave an organism.
- in single-cell organisms simple diffusion is adequate for substance exchange

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

7.1
Why do larger organisms require transport systems?

A

As animals become larger + more active, their cells are too far from exchange membranes or surfaces for substances to simply diffuse to them, so they need gas exchange systems to supply O2 + remove CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

7.2
What are the features of gas exchange systems?
- what makes gas exchange between surfaces efficient

A
  • an increased surface area
  • a thin layer
  • maintain a good concentration gradient by a rich blood supply + ventilation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

7.2
Where does gas exchange occur in humans?

A

human gas exchange occurs in the lungs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

7.2
What is the structure of the human gas exchange system?

A

Air is drawn into lungs through trachea. Trachea divides into 2 bronchi, which further divide into bronchioles, until they terminate in millions of sacs, the alveoli

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

7.2
Where does gas exchange between the blood (in capillaries) + air take place in humans?

A

this step in gas exchange occurs at the alveoli

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

7.2
How are the trachea and bronchioles adapted?

A
  • the trachea is supported by c-shaped cartilage to keep open. Cartilage, smooth muscle + elastic tissue continue into the bronchi
  • the bronchioles have bands of smooth muscle + elastic tissue surrounding them
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

7.2
How is elastic tissue an adaptation?
- what does it do

A

elastic tissue allows the alveoli in lungs to recoil back into shape after expanding
- when they return to their resting size, they help squeeze out air - this is known as the elastic recoil of the lungs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

7.2
What does the trachea lining have, + how are these adapted?

A
  • the trachea has a lining with specific adaptations to prevent particles+ microorganisms entering the lungs
  • ciliated epithelium cells + goblet cells line the trachea
  • goblet cells produce mucus. Ciliated cells move the mucus (+ any trapped particles) up the trachea, until it can be swallowed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

7.2
What are the features of the alveolus?

A

Alveoli maximise gas exchange by:
- having a very large surface area
- being moist to aid diffusion of gases
- having a rich blood supply to maintain a concentration gradient
having very thin walls, like capillaries, so diffusion distance between air in alveoli + blood vessels in capillaries is short

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

7.2
What are the 2 processes in human ventilation?

A
  • inhalation
  • exhalation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

7.2
How does inhalation work?

A
  • the intercostal muscles contract and moves ribs up
  • the diaphragm contracts and flattens
  • the volume of lungs increases
  • air moves into the lungs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

7.2
How does exhalation work?

A
  • the external intercostal muscles relax; when exercising, internal intercostal muscles contract, move ribs down
  • the diaphragm relaxes and moves up
  • the volume of lungs decreases
  • air moves out of the lungs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

7.2
What is inspiration?

A

The thorax volume increases + thoracic pressure decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

7.2
What is expiration?

A

The thorax volume decreases + thoracic pressure increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

7.3
What are the 3 different ways that volume of air drawn in + out of lungs can be measured?

A
  • a peak of low meter
  • vitalographs
  • a spirometer
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

7.3
How does a peak flow meter work?

A

It is a simple device that measures rate at which air can be expelled from lungs
- people who have asthma often use these to monitor how well lungs are working

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

7.3
How does a vitalograph work?

A

They are more sophisticated versions of peak flow meter. The patient being tested breathes out as quickly as they can through mouthpiece, + instrument produces a graph of air amount they breathe out + how quick it’s breathed out
- this volume of air is called the forced expiratory volume in 1 second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

7.3
How does a spirometer work?

A

It is commonly used to measure different aspects of lung volume, or to investigate breathing patterns
- there are many different forms of spirometer but they all use the same principle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

7.3
How can the volume of oxygen be measured in spirometer?

A

Carbon dioxide from exhaled air is absorbed by soda line so that the volume of oxygen used can be measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

7.3
What is the definition of breathing rate?

A

The number of breathes taken per minute (breaths per minute)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

7.3
What are the 5 components of lung volume that can be measured?

A
  • tidal volume
  • vital capacity
  • inspiration reverse column
  • expiratory reverse column
  • residual volume
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

7.3
What is tidal volume?

A

It’s the volume of air that lives into + out of lungs with each resting breath

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

7.3
What is vital capacity?

A

The volume of air that can be breathed I. When the patron gets possible exhalation is followed by deepest possible intake of breath

(The max volume of air that can be exhaled after a max inhalation- dm3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

7.3
What is inspiratory reverse column?

A

It’s the maximum volume of air you can breathe in over + a over a normal inhalation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

7.3
What is expiratory reverse column?

A

It’s the extra amazing of air you can force if your lungs over + above the normal tidal volume of air you breathe out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

7.3
What is residual volume ?

A

It is the volume of air that is left in your lungs when you have exhaled as hard as possible
- this cannot be measured directly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

7.4
What do many insects have along their thorax + abdomen?

A

Many insects have spiracles along their thorax + abdomen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

7.4
How do insects use movement of thorax + abdomen?

A

Insects use the movement to change body volume + move air in and out (ventilation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

7.4
What is the trachea like inside an insect?

A

Inside, the tracheae (tubes) divide until they reach the cells as tracheoles
- the tracheoles are lined with tracheal fluid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

7.4
Where does diffusion occur in insects and how?

A

Diffusion of oxygen and carbon dioxide occurs between body cells + thin walls of the tracheoles
Oxygen + carbon dioxide dissolve in tracheal fluid + diffuse through the thin walls of tracheoles and into the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

7.4
How are grills adapted to maximise efficient gas exchange across them?

A
  • they have a rich blood supply to the gills, to maximise amount of blood that can be oxygenated
  • each gill filament is cover d in many gill lamellae to increase surface area
  • the blood water flow past each other in a countercurrent system, so the conc. of oxygen in water is always higher than in the blood. This maintains a conc. gradient between water and + blood supply along the whole grill
  • ventilation is used to increase water flow over the grills + increase the rate of diffusion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

7.4
How does ventilation occur in fish?

A

Ventilation occurs through the increasing and decreasing volume of the buccal cavity + the opening and closing of the operculum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

7.4
Explain the steps in the ventilation process of a fish

A
  • fish opens its mouth, lowing the floor of buccal cavity, + increasing the volume of buccal cavity
  • this livery’s pressure inside buccal cavity, which forces water into it
  • the operculum is shut
  • fish closes its mouth, reducing volume in buccal cavity
  • pressure inside buccal cavity increases, forcing the water across the grill filaments
  • operculum opens, + water flows out of the grills
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

7.4
What is the countercurrent principle in fish?

A

Blood in capillaries flows in opposite direction to water flowing over them, so oxygen conc. in water is always higher than the oxygen conc. in the blood along the whole gill
- this maximises gas exchange compared with a parallel system, as it maintains a conc. gradient for whole length of the gill lamellae

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

8.1
Why do larger organisms need a circulatory system?

A

As organisms get larger, their surface area to volume ratio decreases and diffusion is no longer sufficient to provide for those needs. So they need a circulatory system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

8.1
What are the different circulatory systems in animals?

A
  • Open circulatory systems.
  • Closed circulatory systems.
  • Single closed circulatory systems
  • Double closed circulatory systems.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

8.1
What is an open circulatory system?
- what animals have it

A
  • It is found in insects and arthropods.
  • Bathe all the cells in a fluid called haemolymph where substance exchange takes place.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

8.1
What is a closed circulatory system?

A

A pump heart and vessels through which blood is circulated between the gas exchange surface and the body cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

8.1
What is a single closed circulatory system?
- what animals have it

A
  • Fish have a single, circular closed circulatory system.
  • Blood is pumped by the heart through the gills to the body and back to the heart.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

8.1
What is a double closed circulatory system?
- what animals have it

A
  • Mammals, birds, amphibians and reptiles have a double closed circulatory system.
  • The blood visits the heart twice in every complete circuit.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

8.2
What are the three main blood vessels?

A
  • Artery
  • Vein
  • Capillary
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

8.2
Describe the structure of an artery.

A

Arteries can withstand high pressures due to their thick walls containing elastic tissue and smooth muscle tissue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

8.2
What are arterioles?
- describe the structure

A

Arterioles are much smaller arteries that deliver blood to capillaries. Arterioles have thinner walls than arteries and less elastic tissue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

8.2
Describe the structure of veins and venules.

A

Venules contain some elastic and muscle tissue, but have thinner walls and a larger lumen compared to arteries. They can contain valves. Valves prevent the backwards flow of blood. Blood from our arterioles flows into capillaries and then back into venules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

8.2
What are capillaries?
- describe the structure

A

Capillaries are very small blood vessels, 4-10 micrometres in diameter. They allow only one red blood cell through at a time. They’re made of a single layer of endothelial cells.
Certain solutes pass across the capillary walls to and from the tissues.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

8.3
What does blood contain?

A
  • It contains plasma with his old glucose, amino acids, mineral ions, hormones, large proteins, e.g. albumin + globulins
  • Also contains red blood cells, platelets and white blood cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

8.3
What do erythrocytes (red blood cells) carry?

A
  • Erythrocytes carry oxygen, carbon dioxide and antigens.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

8.3
What are some functions of blood?

A

The transport of:
- Oxygen to, and carbon dioxide from, the respiring cells.
- Digested food from the small intestine.
- Nitrogenous waste products from the cells to the excretory organs.
- Chemical messages (Hormones)
- Food molecules, from storage compounds to the cells that need them.
- Platelets to damaged areas to clot the blood.
- Cells and antibodies involved in the immune response

50
Q

8.3
What does tissue Fluid contain?

A

It’s the same as blood, but no red blood cells leucocytes (type of white blood cells) or large proteins.

51
Q

8.3
What are lymph vessels?
- What do they contain?

A
  • Lymph vessels are saclike and some tissue fluid drains into them. They have valves and the lymph circulates when skeletal muscles contract.
  • Contains less oxygen, glucose and amino acids, but more carbon dioxide, fatty acids, lymphocytes and antibodies, then blood.
52
Q

8.3
Where is tissue fluid formed?

A

Tissue fluid is formed around the body cells bathing them in solutes. It then drains into lymphatic vessels and eventually back into the bloodstream.

53
Q

8.3
What are the two different kinds of pressure involved in the formation and drainage of tissue fluid?

A
  • Hydrostatic pressure.
  • Oncotic pressure
54
Q

8.3
What is hydrostatic pressure?

A
  • The pressure from the fluid on the walls of the capillary usually forces plasma out of the circulatory system.
55
Q

8.3
What is oncotic pressure?

A
  • Osmotic pressure from proteins in the blood plasma that draws water into the circulatory system.
56
Q

8.3
Why does plasma leave the capillaries at the arteriole end?

A

Plasma leaves the capillary at the art Rio end because the hydrostatic pressure is greater than the oncotic pressure.

57
Q

8.3
Why does most of the tissue fluid move back into the capillary towards the venous ends?

A

Towards the venous ends, most of the tissue fluid moves back into the capillary because the oncotic pressure is greater than the hydrostatic pressure.

58
Q

8.4
What is haemoglobin?

A

Haemoglobin is a protein with quaternary structure and it is made-up of four polypeptide chains which each have a prosthetic haem group.

59
Q

8.4
What contains haemoglobin and what is the function of the cell?

A

Red blood cells contain haemoglobin to transport oxygen from the lungs to the respiring cells.

60
Q

8.4
How is carbon dioxide produced?

A

Carbon dioxide is produced from respiration and is transported in the blood in several ways.

61
Q

8.4
What are the two ways in which carbon dioxide is transported in the blood?

A
  • Most carbon dioxide diffuses into the red blood cells (RBCs)
  • A small number of carbon dioxide molecules dissolve in the blood plasma.
62
Q

8.4
How do most carbon dioxide diffuse into the red blood cells?

A
  • It forms carbonic acid by reacting with water catalysed by carbonic anhydrase.
  • The carbonic acid (H2CO3) dissociates into hydrogen carbonate (HCO3-) ions and hydrogen ions (H+). The hydrogen carbonate ions diffuse out of the RBC into the plasma.
  • This leaves the inside of the RBC with a deficit of negative ions, causing chloride ions to diffuse into the RBC from the plasma.
  • This exchange of ions (HCO3- for Cl-) is known as the chloride shift.
63
Q

8.4
If the carbon dioxide molecules don’t dissolve in the blood plasma, what do they do?

A

Some carbon dioxide molecules also attached directly.

64
Q

8.4
What is the oxygen dissociation curve?
- what is on each axis

A

It is a graph that plots the proportion of haemoglobin in its oxygen-laden saturated form on the vertical axis against the partial pressure of oxygen on the horizontal axis.

65
Q

8.4
What is the oxygen dissociation curve?
- oxygen loading

A

At the alveoli, when the first oxygen molecule binds to the first haem group, the haemoglobin changes shape. This makes it easier to bind a further three oxygen molecules.

66
Q

8.4
What is the oxygen dissociation curve?
- Oxygen dissociation

A
  • At the tissues, oxygen dissociates from the haemoglobin due to low partial pressure of oxygen in the tissues.
  • At high partial pressures of oxygen haemoglobin has a higher affinity for oxygen, therefore has higher saturation levels.
  • At low partial pressures of oxygen, haemoglobin has lower affinity for oxygen, therefore has lower saturation levels.
67
Q

8.4
What is the Bohr effect?

A
  • Haemoglobin oxygen binding affinity is inversely related to the concentration of carbon dioxide in the blood.
  • The dissociation of oxyhemoglobin is higher at the tissues where the partial pressure of carbon dioxide is higher. This is known as the Bohr effect.
  • A developing foetus has foetal haemoglobin, which has a higher affinity for oxygen than adult haemoglobin, so that the foetus is able to receive enough oxygen from the maternal blood via the placenta.
  • Foetal haemoglobin will bond with oxygen at lower partial pressures and concentrations of oxygen compared to adult haemoglobin.
68
Q

8.5
Explain the human circulatory system

A

The heart has two main arteries:
- Pulmonary artery - Transports deoxygenated blood to the lungs.
- Aorta - Sports oxygenated blood to the body.
The heart has two main veins:
- Pulmonary vein - Receives oxygenated blood from the lungs.
- Vena cava - Receives deoxygenated blood from the body.

69
Q

8.5
What is the function of the bicuspid valve?
- where is it found

A

found between left ventricle and left atrium + prevents backflow of blood from left ventricle to left atrium

70
Q

8.5
What is the function of tricuspid valve?
- where is it found

A

found between right ventricle and right atrium + prevents backflow of blood from right atrium to right ventricle

71
Q

8.5
What is the function of semi-lunar valve?
- where is it found

A

found in aorta and pulmonary artery and prevents backflow of blood into ventricles

72
Q

8.5
Describe the structure of the heart

A
  • The heart is made of cardiac muscle and has four chambers - two Atria and two ventricles.
  • Each atrium and ventricle is separated by vows to keep a unidirectional flow of blood.
  • Oxygenated blood is collected in the left atrium, pushed into the left ventricle, which has a thicker, muscular wall, and then pushed through the altar to the whole body.
  • At the same time, deoxygenated blood returns from the body into the right atrium and is pushed into the right ventricle, which contracts, pumping the blood to the lungs via the pulmonary artery.
  • On the outside of the heart there are visible blood vessels, the coronary arteries and veins. The heart can be dissected to reveal the internal structure.
73
Q

8.5
What is the pathway in which blood takes?

A

Vena cava → R atrium → tricuspid valve → R ventricle → pulmonary semilunar valve → pulmonary artery → lungs → pulmonary vein → L atrium → bicuspid valve → L ventricle → aortic semilunar → aorta → body

74
Q

8.5
What is the cardiac cycle

A

The human circulation system is closed and so the pressure can be regulated.

75
Q

8.5
When does aortic pressure rise?
- what does it create

A
  • Aortic pressure rises when ventricles contract’s blood is forced into the aorta.
  • It then gradually falls, but never below around 12 kPa because of the electricity of its walls.
  • This creates a recoil action - essential if blood is to be constantly delivered to the tissues.
  • Recoil produces a temporary rise in the pressure at the start of the relaxation phase.
76
Q

8.5
When is atrial pressure highest?
- what does it cause

A
  • Atrial pressure is always relatively low because the thin walls of the atrium cannot create much force.
  • It is highest when they’re contracting, but drops when the left atrioventricular valve closes and its walls relax.
  • The Atria then fill up with blood, which leads to a gradual build up of pressure until a slight drop when the left atrioventricular valve opens and some blood moves into the ventricle.
77
Q

8.5
When does ventricular pressure rise?
- what are the effects

A
  • Ventricular pressure is low at first, but gradually increases as the ventricles fill with blood as the Atria contract.
  • The left atrioventricular valves close and pressure rises dramatically as the thick, muscular walls of the ventricle contract.
  • As pressure rises above that of the aorta, blood is forced into the altar past the semilunar valves. Pressure falls, as the ventricles empty and the rules relax.
78
Q

8.5
When does ventricular volume rise?
- what are the effects

A
  • Ventricular volume rises as the Atria contract and the ventricles fill with blood and then drops suddenly as blood is forced out into the water when the semilunar valves open.
  • Volume increases again as the ventricles fill with blood.
79
Q

8.5
What is an ECG?
- what does it measure

A

An ECG is a trace of the electrical activity of the heart. A normal trace is made-up of five features (PQRST)

80
Q

8.5
What are the 4 heart rhythm abnormalities that show up on ECG’s

A
  • Tachycardia
  • Bradycardia
  • Ectopic heartbeat
  • Atrial fibrillation
81
Q

8.5
What is Tachycardia?

A

When the heartbeat is very rapid, over 100 bpm

82
Q

8.5

What is Bradycardia?

A

When the heart rate slows down to below 60 bpm

83
Q

8.5
What is an Ectopic heartbeat?

A

Extra heartbeats that are out of the normal rhythm.

84
Q

8.5
What is Atrial fibrillation?

A

This is an example of an arrhythmia, which means an abnormal rhythm of the heart.

85
Q

9.1
What can unicellular organisms rely on for transportation around them?

A

Unicellular plants (phytoplankton) have a large SA:V and can rely on diffusion for transport of nutrients into them + removal of waste out of them

86
Q

9.1
Why are transport systems important for multicellular organisms?

A

Transport systems are essential to supply nutrients to , and remove waste from, individual cells, when plants become larger and more complex

87
Q

9.1
What does the supply of nutrients from soil rely on?

A

The supply nutrients from soil relies upon the flow of water through a vascular system, as does the jugement of the products of photosynthesis

88
Q

9.1
What are the transport vessels in plants?

A

Plants transport water, sugars + mineral ions using xylem and phloem tissues

89
Q

9.1
What is the function of the xylem tissue in plants?

A

Xylem vessels transport water in roots, stem + leaves of plant
- this happens in one direction only, from roots to top of the plant

90
Q

9.1
What is the function of the phloem tissue in plants?

A

Transports organic molecules, such as sucrose form photosynthesis
- this can happen in all directions

91
Q

9.1
How are the xylem and phloem arranged?

A

Xylem + phloem are arranged in vascular bundles. Roots have a single vascular bundle, which branches into a separate arrangement of tubes up the stem
Further branching into veins of xylem + phloem in leaves. The structural supporting tissue is called the cortex

92
Q

9.2
What is the function of a xylem?
- describe the structure

A
  • Xylem vessels transport water and dissolved minerals to the issues that need them.
  • It is made from dead lignified cells that form continuous tubes.
  • So contains pits which connect one Xylem vessel to another to allow lateral water movement.
93
Q

9.2
How does water move through the transpiration stream?
- adhesion
- cohesion

A
  • Moves from the soil into the root hair cells by osmosis, then moves through the roots to the Xylem vessel.
  • Water evaporates from the leaves and surface tension causes cohesion between water molecules (cohesion-tension theory) which pulls other water molecules up the stem.
  • Water also adheres to the side of the Xylem vessels, creating a continuous transpiration stream.
94
Q

9.2
What is the apoplast pathway stopped by?

A
  • The apoplast pathway is stopped by their Casparian strip, which is found in the endodermal layer of the root.
  • This causes all water to enter cells to travel further through the plant.
95
Q

9.2
What are three pathways taken by water?

A
  • Apoplast: water travels between cells via mass flow
  • Symplast: water enters cells via osmosis
  • vacuolar: water passes through cell vacuoles.
96
Q

9.3
What is transpiration?
- why is it inevitable
- why is it vital
- how can it be regulated

A

It is water vapour loss from stems and leaves via the stomata by evaporation AND diffusion.
- it is inevitable as the stomata must be open for gas exchange, to enable photosynthesis to occur.
- it is vital as it pull water up the plant, so it can be transported to all cells
- transpiration can be regulated through closing and opening the stomata

97
Q

9.3
Where are the stomata located?

A

Stomata are pores in leaves, located on the underside of leaves

98
Q

9.3
What are the steps in the transpiration process?

A

1) Water evaporates from the surface of cells into air spaces of the spongy mesophyll layer
2) Water leaves the leaves through diffusion through the stomata, down a water vapour potential gradient.
3) Cohesion of water molecules to each other and adhesion to the Xylem vessel walls and tension (negative pressure) maintains the flow of water through the Xylem.

99
Q

9.3
What is the Cohesion-tension theory?

A
  • It is the best current model explaining movement of water up a plant, explained by negative pressure (tension) in the xylem, + cohesive and adhesive properties of water, enabling a continuous stream.
100
Q

9.3
What is the Transpiration pull?

A

It is a force that causes tension in the Xylem due to water loss.

101
Q

9.3
What is a transpiration stream?

A

It is the continuous movement of water up a plant.

102
Q

9.3
How do you investigate transpiration?
- what equipment is used
- what is it used to investigate

A
  • Due to stomata being open for gas exchange water vapour is lost from the plant via transpiration.
  • Different environmental conditions like humidity can affect the rate of transpiration.
  • The effects of these conditions can be investigated using a Potometer.
103
Q

9.3
How do you investigate transpiration?

A
  • A cut, leafy shoot is connected to a rubber tube and a graduated capillary tube with a water reservoir in between.
  • The rate of water uptake is measured by the distance between the bubble travels in the capillary tube, which we assume is equivalent to transpiration rate.
104
Q

9.3
What are five possible factors that can affect the rate of transpiration?

A
  • Light intensity.
  • Temperature.
  • Air movement/wind.
  • Relative humidity.
  • Soil-water availability.
105
Q

9.3
How does an increase in light intensity affect the rate of transpiration?

A

Increased light intensity → solutes are pumped into guard cells → increased turgor → guard cells only swell at outer ends, causing bending → stomata open stomata, regular gas exchange, and water loss.
- Pumping solids into guard cells (only expands lengthways) decreases their water potential.
- Water moves down a water potential gradient an into guard cells by osmosis, increasing turgor (pressure)
- Hormones: When water is scarce, hormones can trigger a reduction in turgor of guard cells to close stomata.

106
Q

9.3
How does an increase in temperature affect the rate of transpiration?

A

An increase in temperature increases the rate of transpiration: Water molecules in cells of spongy mesophyll gain kinetic energy.
- And increasing the temperature increases the rate because: Higher temperatures increase the amount of water the air can hold. This reduces the relative humidity of air, reducing the water potential.

107
Q

9.3
What is the definition of relative humidity?

A

Relative humidity is a measure of the amount of water in the air compared to the maximum it can hold.

108
Q

9.3
What effect does increasing temperature have on the relative humidity?

A

Increasing temperature decreases the relative humidity, which causes a decrease in the water potential, increasing the water vapour potential gradient.

109
Q

9.3
How does an increase in air movement/wind affect the rate of transpiration?

A

Increasing air movement increases the rate of transpiration: Water molecules sometimes trapped in still air outside of stomata are blown away. There is a higher water vapour potential gradient in the leaf, so more diffuses out of stomata.

110
Q

9.3
How does an increase in relative humidity affect the rate of transpiration?

A

Increasing relative humidity decreases the rate of transpiration: A higher water vapour potential outside the leaf, so the lower the diffusion gradient and therefore decreases the rate of diffusion.

111
Q

9.3
How does an increase in soil-water availability affect the rate of transpiration?

A

Increasing soil-water availability increases the rate of transpiration: If a plant is under water-stress rates will be reduced.

112
Q

9.4
What is translocation?

A

plants transport sucrose and other substances from sources (e.g. leaf cells) to sinks (e.g. roots, meristem)

113
Q

9.4
Describe the structure of phloem

A
  • Phloem is made-up of living cells called sieve tube elements, which have perforated cell walls called Sieve plates between them and companion cells beside them.
  • Companion cells regulate the movement of solutes and provide ATP for active transport. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell.
114
Q

9.4
What is the function of phloem?

A
  • Phloem transports organic molecules (assimilates) both up and down the plant.
  • This is an active process requiring energy in the form of ATP, to move these substances.
115
Q

94
What are assimilates?

A

They are organic molecules that are transported within a plant
- e.g organic molecules like glucose, produced during photosynthesis

116
Q

9.4
What is phloem loading?

A
  • At a source, usually a photosynthesising leaf, sucrose is loaded into the phloem.
  • The companion cells use proton pumps to pump out hydrogen ions using ATP, creating a high concentration of hydrogen ions outside the companion cell.
  • A co-transporter protein in the companion cell membrane then transports these hydrogen ions back into the cell in conjunction with sucrose molecules.
  • Sucrose then diffuses from the companion cell into the sieve tube elements via plasmodesmata.
  • Water moves via osmosis from their companion cell to the sieve tube elements due to the water potential gradient set up by the movement of sucrose into the sea, two elements previously.
117
Q

9.4
What is phloem unloading?

A
  • At a sink - for example, a root - the sucrose moves out of the sieve tube elements by diffusion.
  • The concentration gradient is maintained by converting sucrose into glucose and fructose.
  • Loading and unloading causes mass flow through the phloem via hydrostatic pressure and a pressure gradient.
118
Q

9.5
What are two types of plants living in extremes?

A
  • Xerophytes
  • Hydrophytes
119
Q

9.5
How are xerophytes adapted to live in an extreme environment to conserve water?

A
  • Grow in dry habitats (e.g. Cacti, marram grass)
  • Thicker cuticle
  • Reduced leaf surface area (e.g. needles)
  • Few sunken stomata.
  • Rolled leaves (e.g. marram grass)
120
Q

9.5
How are hydrophytes adapted to live in an extreme environment?

A
  • Grow in or on water (e.g. water lilies)
  • Little or no waxy cuticle.
  • Large flat leaves.
  • Minimal root system.
  • Air pockets to aid floatation and flexible stems.

OCR Biology A level (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions