Transport

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Blood Vessels: Capillaries

Capillaries form capillary beds that provide the exchange surface between blood and tissues.
Walls are one cell thick (single layer of endothelial cells), reducing diffusion distance for oxygen and carbon dioxide.
Some capillaries have fenestrations (gaps) that allow blood plasma to leak out and form tissue fluid.
Tissue fluid surrounds cells and enables exchange of oxygen, glucose, and other small molecules; large proteins cannot fit through fenestrations.
Capillaries have a narrow lumen, forcing red blood cells to travel in single file, slowing blood flow and increasing opportunity for diffusion.
Capillaries branch between cells, increasing surface area for diffusion and bringing blood close to cells.

The blood vessel network

Blood Vessels: Arteries

Arteries transport blood away from the heart at high pressure.
Walls have three layers: an inner endothelial layer (smooth, reduces friction), a middle layer of smooth muscle and elastic tissue, and an outer layer of collagen and elastic fibres.
The thick muscle layer strengthens arteries to withstand high pressure and can contract or relax to regulate lumen diameter and blood pressure.
Elastic tissue stretches and recoils to even out pressure fluctuations as the heart beats.
Collagen prevents over-stretching and rupturing of the arterial wall as blood surges from the ventricles.
Arteries have a narrow lumen to help maintain high blood pressure.
Systolic pressure is the peak pressure in arteries when blood is forced out of ventricles; diastolic pressure is the lowest pressure when the heart relaxes.
Vasoconstriction (decreased lumen diameter) increases blood pressure; vasodilation (increased lumen diameter) decreases it.

Comparing arteries and veins

Blood Vessels: Veins

Veins transport blood towards the heart at low pressure.
The middle layer is much thinner than in arteries because veins do not need to withstand high pressure.
Veins have valves that prevent backflow of blood under low pressure.
Walls are flexible, allowing surrounding skeletal muscles to compress them and push blood towards the heart.
Veins have a wide lumen, maximising blood volume flow and reducing friction between blood and the endothelial layer.
The rate of blood flow is slower in veins, but the larger lumen means the volume delivered per unit time is equal to that in arteries.

The main blood vessels of the body

Identifying Blood Vessels in Micrographs

Arteries have thick walls (more collagen, elastic fibres, and smooth muscle) and a narrow lumen relative to wall thickness.
Veins have thin walls and a wide lumen relative to wall thickness.
These characteristics can be used to distinguish arteries and veins in micrographs.

Measuring Pulse Rate

The contraction of ventricles forces blood through arteries, causing them to expand; this is felt as a pulse.
Pulse can be measured at the carotid artery (side of neck, below jaw) or radial artery (wrist, below base of thumb).
To measure pulse: place two fingers on the artery, gently compress, and count pulses for 60 seconds (or 30 seconds and multiply by 2).
Do not use your thumb because it has its own pulse, which can lead to inaccurate results.
Digital devices such as data loggers, smartwatches, or fitness bands can also measure pulse rate by scanning blood flow through the radial artery.

Monitoring heart rate

Coronary Heart Disease

Occlusion is the narrowing of arteries due to a blockage.
Atherosclerosis begins with damage to artery walls (e.g., from high blood pressure), leading to build-up of fatty deposits called atheromas under the endothelium.
Atheromas narrow the lumen, reducing blood flow and increasing blood pressure, which causes further damage.
Fibrous tissue repairs damage but is not elastic, reducing artery elasticity; the smooth lining breaks down forming plaques.
Rupture of plaques can lead to blood clotting; a clot within a vessel is a thrombus, and a circulating clot is an embolus.
An embolus blocking a small artery causes tissues downstream to lack oxygen and nutrients, leading to cell death; in coronary arteries this can cause a myocardial infarction (heart attack).
Treatment for blocked coronary arteries includes heart bypass surgery, using a blood vessel from the patient's leg to create an alternative route.

The coronary arteries

Evaluating Data on Coronary Heart Disease

Epidemiological studies provide correlation data, not definite causal links between risk factors (e.g., saturated fat intake) and coronary heart disease.
Clinical studies of individual patients are often small and may not be representative.
Controlled experiments (e.g., comparing normal diet vs high saturated fat diet) are not possible due to ethical considerations.
When evaluating data, consider: sample size and representativeness, use of human subjects, statistical significance, presence of a control group, and replication.
Control variables (e.g., prior health, lifestyle, age, sex) increase validity; researchers should not be biased, and data collection must be accurate.
Correlation is an association between variables; it does not necessarily imply causation.
The correlation coefficient (r) indicates strength of relationship: closer to 1 or -1 is stronger; 0 means no correlation.

The Transpiration Stream

Water evaporates from leaf cells during transpiration, drawing water from the nearest xylem vessels.
Water molecules adhere to cell walls, enabling movement through cell walls; this is capillary action.
Loss of water from xylem generates tension (negative pressure) within the xylem.
Cohesion between water molecules transmits the pulling force down the stem to the roots; this is transpiration pull (cohesion-tension theory).
The continuous upward flow of water in xylem is the transpiration stream.
Transpiration cools the plant via evaporative cooling, helps uptake of mineral ions, and provides turgor pressure for support.

Transpiration through a leaf

Adaptations of Xylem Vessels

Xylem vessels transport water and mineral ions from roots to leaves.
Mature xylem vessels are non-living, with no cell contents or end walls, forming long, continuous, hollow tubes for unimpeded flow.
Walls are thickened with cellulose and strengthened with lignin, making them tough and able to withstand very low internal pressures (tension) without collapsing.
Walls contain pits (tiny pores) that allow water to enter and move sideways between vessels; if one vessel is damaged, water can flow into another.

Vascular tissue in a plant

Drawing Root & Stem Structure

In a dicotyledonous stem, tissues include: epidermis (outer layer, prevents water loss), parenchyma (cortex and pith, store starch), and vascular tissue in a ring of vascular bundles.
In stem vascular bundles, xylem is on the outer part of the ring and phloem on the inner part.
In a dicotyledonous root, xylem is centrally located in a cross-shaped structure, with phloem bundles between the arms of the xylem.
Root cortex consists of parenchyma cells storing starch; epidermis forms outer layer; root hairs are specialised epidermal cells absorbing water and mineral ions.
The endodermis forms the boundary between vascular tissue and cortex in a root.
When drawing plan diagrams: do not draw individual cells, use clear continuous lines, avoid shading, pay attention to proportions, label clearly, and add a scale bar or estimated size.
Annotate drawings with the main functions of the labelled structures.

Root hair cells: structure and location

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Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 59 câu hỏi. Đăng ký để xem tất cả.

1.Which blood vessel carries blood away from the heart?
Easy
- AArtery
- BVein
- CCapillary
- DVenule
2.Which blood vessel has walls that are one cell thick?
Easy
- AArtery
- BVein
- CCapillary
- DArteriole
3.Veins contain valves to prevent the backflow of blood.
Easy
True or false?
4.Arteries have a wider lumen than veins.
Easy
True or false?
5.What is the main function of the elastic tissue in the wall of an artery?
Easy
- ATo contract and relax to control the diameter of the lumen
- BTo stretch and recoil to maintain blood pressure
- CTo reduce friction between blood and the vessel wall
- DTo allow exchange of gases between blood and tissues
6.Which structure in a capillary allows blood plasma to leak out and form tissue fluid?
Easy
- AValves
- BFenestrations
- CElastic fibres
- DSmooth muscle cells
7.Which of the following are characteristics of capillaries? (select all that apply)
Medium
- AWalls are one cell thick
- BHave a narrow lumen
- CContain valves
- DHave fenestrations
- EHave a thick layer of smooth muscle
8.Which of the following best defines systolic pressure?
Medium
- AThe lowest pressure reached in the arteries as the heart relaxes
- BThe peak pressure reached in the arteries as blood is forced out of the ventricles
- CThe pressure in the veins when skeletal muscles contract
- DThe pressure in the capillaries during exchange of substances

Thêm câu hỏi

9.What is the definition of occlusion in the context of coronary heart disease?
Medium
- AThe widening of arteries due to relaxation of smooth muscle
- BThe narrowing of arteries due to a blockage
- CThe formation of a blood clot in the veins
- DThe inflammation of the artery wall
10.Which of the following is a consequence of atherosclerosis in the coronary arteries?
Medium
- AReduced blood flow to the heart muscle, leading to a heart attack
- BIncreased elasticity of the artery walls
- CDecreased blood pressure in the arteries
- DIncreased oxygen supply to the heart muscle
11.The transpiration stream is the continuous upward flow of water in the xylem vessels of plants.
Easy
True or false?
12.Xylem vessels are living cells at maturity.
Easy
True or false?
13.In a transverse section of a dicotyledonous root, how is the xylem arranged?
Medium
- AIn a ring of vascular bundles
- BIn a central cross-shaped structure
- CScattered throughout the cortex
- DJust inside the epidermis
14.Which tissue in a dicotyledonous stem forms the outer layer?
Medium
- ACortex
- BPith
- CEpidermis
- DVascular bundles
15.Which of the following are functions of the smooth muscle layer in the wall of an artery? (select all that apply)
Medium
- AContracting to reduce the diameter of the lumen and increase blood pressure
- BRelaxing to increase the diameter of the lumen and decrease blood pressure
- CStretching and recoiling to even out pressure fluctuations
- DStrengthening the artery wall to withstand high pressure
- ESecreting collagen to prevent over-stretching
16.Which of the following are adaptations of xylem vessels for the transport of water? (select all that apply)
Medium
- AThey are living cells with cytoplasm
- BThey are hollow tubes lacking cell contents and end walls
- CTheir walls are thickened with cellulose and strengthened with lignin
- DThey contain pits that allow water to move sideways between vessels
- EThey have valves to prevent backflow
17.Which of the following statements about the arrangement of tissues in a transverse section of a dicotyledonous root are correct? (select all that apply)
Medium
- AThe xylem is centrally located in a cross-shaped structure
- BThe phloem is arranged between the arms of the xylem
- CThe vascular tissue is arranged in a ring of vascular bundles
- DThe endodermis forms the boundary between the vascular tissue and the cortex
- EThe epidermis forms the central region of the root
18.Match each blood vessel type with its correct description.
Medium
- Artery
- Vein
- Capillary
- Thick muscular wall and narrow lumen
- Thin wall and wide lumen with valves
- Wall one cell thick with fenestrations
19.Match each term with its correct definition.
Medium
- Systolic pressure
- Diastolic pressure
- Occlusion
- Peak pressure reached in arteries when ventricles contract
- Lowest pressure in arteries when the heart relaxes
- Narrowing of an artery due to a blockage
20.Match each component of blood vessel walls with its role.
Medium
- Elastic tissue
- Collagen
- Smooth muscle
- Stretches and recoils to maintain blood pressure
- Provides strength to prevent over-stretching
- Contracts to narrow the lumen and raise pressure
21.Place the following blood vessels in the order that blood flows through them, starting from the heart and returning to the heart.
Medium
- Aorta
- Arterioles
- Capillaries
- Venules
- Veins
22.Arrange the following steps in the development of atherosclerosis in the correct sequence.
Medium
- Damage to the artery wall due to high blood pressure
- Build-up of fatty deposits (atheromas) under the endothelium
- Narrowing of the lumen and increased blood pressure
- Fibrous tissue repair reducing elasticity
- Plaque formation and possible thrombus
23.Which of the following is the correct definition of capillary action?
Medium
- AThe movement of water through a narrow tube due to adhesion to the walls
- BThe loss of water vapour from the leaves of a plant
- CThe transport of sugars through the phloem
- DThe active uptake of mineral ions by root hairs
24.In the cohesion-tension theory, what is the direct cause of the tension (negative pressure) in the xylem?
Medium
- AThe active pumping of water by root cells
- BThe evaporation of water from the leaf cells
- CThe contraction of the plant stem
- DThe osmotic uptake of water by the roots
25.Which of the following is a function of the endodermis in a dicotyledonous root?
Medium
- ATo absorb water and mineral ions from the soil
- BTo store starch and other substances
- CTo form the boundary between the vascular tissue and the cortex
- DTo transport organic solutes from the leaves
26.Veins have a wider lumen than arteries.
Easy
True or false?
27.The elastic tissue in artery walls stretches and recoils to help maintain blood pressure.
Easy
True or false?
28.A student counts a pulse of 34 beats in 30 seconds. What is the pulse rate in beats per minute?
Medium
- A34 bpm
- B68 bpm
- C102 bpm
- D17 bpm
29.A micrograph of a blood vessel shows a wall that is very thick relative to the diameter of the lumen, and the lumen itself is narrow. Which vessel is this most likely to be?
Medium
- AA vein
- BAn artery
- CA capillary
- DA venule
30.A patient's coronary artery has an atherosclerotic plaque that reduces its lumen diameter from 3.2 mm to 1.6 mm. By what percentage has the cross-sectional area of the lumen been reduced?
Hard
- A25%
- B50%
- C75%
- D87.5%
31.A study finds a correlation coefficient of r = −0.82 between the amount of soluble fibre eaten per day and blood cholesterol concentration. What is the best interpretation of this result?
Medium
- AEating more soluble fibre causes blood cholesterol to fall.
- BThere is a strong negative correlation: as fibre intake increases, cholesterol tends to decrease.
- CThere is no relationship between fibre intake and cholesterol.
- DThe data prove that fibre has no effect on cholesterol.
32.A scientist is designing a controlled trial to test whether a new drug reduces the risk of coronary heart disease. Which features would improve the validity of the results? (select all that apply)
Medium
- AUsing a large sample size
- BIncluding a control group that does not receive the drug
- CControlling factors such as age, sex and exercise levels
- DPublishing the results after only one small trial
- EEnsuring the sample comes from a single age group and sex
33.Vasodilation of the circular muscle in an artery wall increases the diameter of the lumen and decreases blood pressure.
Easy
True or false?
34.Match each blood vessel with the correct description of its wall and lumen.
Medium
- Artery
- Vein
- Capillary
- Thick muscular wall with a narrow lumen
- Thin wall with a wide lumen and valves
- Wall one cell thick with a very narrow lumen
35.Which transport process is directly interrupted by girdling?
Medium
- ATranslocation of organic solutes in the phloem
- BTranspiration pull in the xylem
- CCapillary action in the leaf cell walls
- DCohesion between water molecules
36.A student measures their pulse rate by placing two fingers on the radial artery at the wrist. Why should the thumb not be used to take a pulse?
Medium
- AThe thumb has its own pulse, which can be felt and lead to an inaccurate count
- BThe thumb cannot detect a pulse because it has too few nerve endings
- CUsing the thumb blocks the radial artery completely
- DThe thumb is too small to compress the artery effectively
37.A student counts 26 beats in 30 seconds while measuring their pulse at the carotid artery. What is their pulse rate in beats per minute?
Medium
- A52
- B26
- C78
- D13
38.In a controlled trial testing whether plant sterols reduce the risk of coronary heart disease, volunteers were randomly divided into two groups. One group ate plant sterols daily for eight weeks. How should the control group have been treated?
Medium
- AGiven a placebo with no plant sterols, but otherwise treated identically
- BGiven nothing at all and not monitored during the eight weeks
- CGiven a higher dose of plant sterols to compare with the experimental group
- DAllowed to choose their own diet for the eight weeks
39.A study reports a correlation coefficient of r = −0.82 between daily soluble fibre intake and blood cholesterol concentration. Which statements about this result are correct? (select all that apply)
Hard
- AThere is a strong negative correlation between the two variables
- BAs soluble fibre intake increases, blood cholesterol concentration tends to decrease
- CThe result proves that soluble fibre causes a reduction in blood cholesterol
- DA correlation coefficient of −0.82 indicates no relationship between the variables
- EThe closer r is to −1, the stronger the negative relationship
40.A larger sample size in an epidemiological study is more likely to be representative of the population.
Easy
True or false?
41.Complete the sentence about capillary structure.
Easy
Capillary walls are made from a single layer of ____ cells.
42.Complete the sentence about vein structure.
Easy
Veins have a ____ lumen to maximise the volume of blood that can flow at any one time.
43.Name the blood vessel that carries blood from the heart to the tissues of the body.
Medium
44.Identify the blood vessel with the greatest decrease in mean blood pressure according to the table.
Medium
45.Complete the sentence about xylem structure.
Easy
Xylem vessel walls are strengthened by a polymer called ____.
46.Name the process by which water evaporates from the leaves of a plant.
Easy
47.The mean blood pressure in the aorta is 94 mmHg and in the vena cava is 2 mmHg. Calculate the symmetrical percentage difference between these two values. Give your answer to three significant figures.
Medium
48.Complete the sentence about the structure of capillaries.
Easy
Capillary walls are made from a single layer of ____ cells.
49.Complete the sentence about the transpiration stream.
Medium
The continuous upward flow of water in the xylem vessels of plants is known as the ____.
50.Complete the sentence about the cohesion-tension theory.
Medium
The pulling force transmitted through the xylem due to cohesion between water molecules is known as ____.
51.Name the tissue that transports organic solutes from the leaves to other parts of the plant.
Easy
52.A pulse is counted for 15 seconds and 19 beats are felt. Calculate the pulse rate in beats per minute.
Medium
53.Explain how the structure of xylem vessels is adapted for the transport of water.
Hard
54.Describe the role of hydrogen bonding in the cohesion-tension theory of water transport in the xylem.
Hard
55.Explain how the structure of capillaries is adapted for efficient exchange of materials between the blood and tissues.
Hard
56.Explain how girdling may kill a tree over time.
Hard
57.Describe the role of hydrogen bonding in the cohesion-tension theory of water transport in the xylem of plants.
Hard
58.The mean blood pressure in the aorta is 94 mmHg and in the vena cava is 2 mmHg. Calculate the symmetrical percentage difference between these two values. Give your answer to three significant figures.
Medium
- A172 %
- B191 %
- C210 %
- D229 %
59.A pulse is counted for 15 seconds and 19 beats are felt. Calculate the pulse rate in beats per minute.
Medium
- A68 bpm
- B84 bpm
- C92 bpm
- D76 bpm

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