Transport (DP IB Biology)

The arterial walls are much thicker than those of veins.

Lumen is the internal space or cavity within a blood vessel through which blood flows.

False.

The lumen of arteries is relatively narrow compared to the thickness of the wall.

The larger lumen in veins helps to ensure that blood returns to the heart at an adequate speed by reducing friction between the blood and the endothelial layer.

In veins, the rate of blood flow is slower, but the larger lumen means the volume of blood delivered per unit of time is equal to that of arteries.

A pulse in arteries is caused by the expansion of arteries to accommodate the large volume of blood forced through them by the contraction of the ventricles.

Carotid artery is an artery that runs down the side of the neck, where a pulse can be felt just below the jaw.

False.

You should not use your thumb when taking a pulse, as it also has a pulse that can lead to inaccurate results.

To count pulse rate manually, place two fingers on the radial or carotid artery, gently compress the blood vessel, and count the number of pulses felt for 60 seconds.

Two examples of digital devices that can be used to measure pulse rate are data loggers and smartwatches / fitness bands.

Occlusion of the arteries is the narrowing of the arteries due to a blockage.

Atherosclerosis is a process where fatty deposits build up under the endothelium of arteries, narrowing the lumen and reducing blood flow.

False.

Fibrous tissue produced to repair artery wall damage is not elastic, so it reduces the overall elasticity of the artery wall.

A thrombus is a blood clot formed within a blood vessel.

Embolus is a blood clot that circulates in the bloodstream.

A myocardial infarction, or heart attack, occurs when parts of the heart muscle die due to blocked coronary arteries.

False.

Epidemiological studies provide correlation data and do not provide a definite causal link between coronary heart disease and risk factors.

A larger sample size is more likely to be representative as it covers a larger cross-section of the population.

Validity in scientific studies means that the results measure what they set out to measure, are not influenced by external variables or poor experimental design, and have been analysed correctly.

The correlation coefficient (r) indicates the strength of the relationship between variables.

A correlation coefficient of 1 or -1 indicates a perfect correlation, where all data points lie on a straight line.

False.

A perfect correlation coefficient does not prove a causal link.

Transpirational pull is the pulling force created by the tension in the xylem when water moves into leaf cells, transmitted through the plant via cohesion between water molecules.

Capillary action is the movement of water that occurs due to adhesion to the walls of a narrow tube, such as the cell walls in plant xylem.

The cohesion-tension theory of transpiration explains how water moves upwards through plants against gravity, due to the tension created by water loss in leaves and the cohesion between water molecules.

False.

The transpiration stream is a continuous upwards flow of water in the xylem vessels of plants.

Transpiration is important to plants in three ways:

1. it provides cooling through evaporation

2. helps in the uptake of mineral ions

3. provides support to leaves and non-woody stems through turgor pressure

The two main functions of xylem vessels are the transport of water and the transport of mineral ions from the roots.

Lignin is a polymer that strengthens the walls of xylem vessels, making them extremely tough and able to withstand very low internal pressures without collapsing.

False.

Mature xylem vessels are non-living cells, with their cell contents broken down to form long, continuous, hollow tubes.

Pits are tiny pores in xylem vessel walls that allow water to enter and move sideways between vessels, ensuring continued water flow if a vessel is damaged.

Two structural adaptations of xylem vessels that facilitate water transport are:

1. They are long, continuous, hollow tubes without cell content or end walls, allowing unimpeded flow

2. Their walls are thickened with cellulose and strengthened with lignin, enabling them to withstand very low internal pressures

The epidermis in a dicotyledonous stem prevents water loss and provides protection from herbivores.

In a dicotyledonous stem, xylem forms the outer part of the ring of vascular bundles, while in a root, it is centrally located in a cross-shaped structure.

False.

In a plan diagram, only the outlines of different tissues are drawn, not individual cells.

Endodermis is the layer that forms the boundary between the vascular tissue and cortex in a root.

False.

Shading should be avoided when drawing plan diagrams of stems or roots.

In a dicotyledonous root, phloem bundles are arranged between the cross "arms" of xylem.

Two key elements that should be included in a plan diagram of a stem or root are:

1. A scale bar or estimated size of the drawing

2. Clear labels for different tissues

The root cortex surrounds the vascular bundle with the epidermis around the outside of the cortex, separating it from the external environment.

Plasma is a straw-coloured liquid that constitutes around 55% of the blood. It is largely composed of water (95%).

Tissue fluid is formed when some plasma is forced out through gaps in the walls of the capillaries to surround the body's cells.

Tissue fluid contains fewer proteins and cells than plasma, as proteins and blood cells are too large to pass through the capillary walls.

Tissue fluid bathes the cells of the body that are outside the circulatory system, and allows the exchange of substances between cells and the blood.

Pressure filtration is the process by which tissue fluid is forced out of the capillaries at the arterial end due to high blood pressure.

At the venous end, the reduced blood pressure allows around 90% of the fluid lost at the arterial end to be reabsorbed back into the capillaries.

The remaining 10% of tissue fluid is collected by lymph vessels and eventually returned to the circulatory system.

The increased protein concentration in the capillary creates a solute gradient that draws water back into the capillary by osmosis.

At the arterial end, the outward force of high blood pressure overcomes the inward pull of the solute gradient, forcing fluid out of the capillaries.

At the venous end, the inward force of the solute gradient overcomes the reduced blood pressure, drawing fluid back into the capillaries.

Some of the tissue fluid enters the lymph capillaries, which are part of the lymphatic system and separate from the circulatory system.

The lymph capillaries have closed ends and large pores that allow large molecules to pass through, and they contain fluid known as lymph.

The lymph fluid moves along the larger lymph ducts by compression caused by body movement, with valves preventing backflow. The lymph eventually re-enters the bloodstream through veins near the heart. Lymph nodes along the ducts contain immune cells that can engulf bacteria.

A closed circulatory system is one where the blood is contained within a system of blood vessels.

The circulatory system for bony fish has a single circulatory path, while the system for mammals is double and has the separation of pulmonary and systemic circulation through the four-chambered heart.

In single circulation, the blood moves through the heart once during each complete circuit. The heart has two chambers, and the blood enters the heart from the body before being pumped to the gills for oxygenation.

In double circulation, the blood flows through the heart twice for each complete circuit of the body. The heart has four chambers - two on the right that pump deoxygenated blood to the lungs, and two on the left that pump oxygenated blood around the systemic circulation.

The advantages include keeping oxygenated and deoxygenated blood separate, maintaining a high pressure for the transport of oxygenated blood, and pumping blood at a lower pressure in the lungs to avoid damaging the delicate blood vessels.

Cardiac muscle is a specialised form of muscle tissue that can contract repeatedly and continuously without becoming fatigued.

The four chambers are the right and left atria (upper chambers) and the right and left ventricles (lower chambers).

The atria receive blood from the veins returning from the lungs and body, and pump it into the ventricles below.

The ventricles receive blood from the atria and pump it out to the lungs (right ventricle) and body (left ventricle).

The septum is a wall of muscular tissue that separates the left and right sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

The pacemaker, or sinoatrial node (SAN), is a region in the right atrium that initiates the heartbeat by sending a wave of excitation across the atria.

The vena cava and pulmonary vein bring blood to the heart, while the pulmonary artery and aorta take blood away from the heart.

The atrioventricular valves (tricuspid and bicuspid) prevent blood from flowing back from the ventricles into the atria.

The semilunar valves (pulmonary and aortic) prevent blood from flowing back from the arteries into the ventricles.

The coronary arteries supply the heart muscle with oxygenated blood for aerobic respiration.

The cardiac cycle is the series of events that take place in one heartbeat, including muscle contraction and relaxation.

True.

The heart will beat without any external stimulus from the nervous system.

Myogenic means the heart will beat without any external stimulus from the nervous system.

The sinoatrial node (SAN) is a group of cells in the wall of the right atrium that controls the cardiac cycle by acting as the pacemaker.

The atrioventricular node (AVN) is a region of conducting tissue between the atria and ventricles.

The bundle of His is a collection of conducting tissue located in the septum.

Systole is the contraction of the heart muscle.

Diastole is the relaxation of the heart muscle.

An atrioventricular (AV) valve is a valve that allows blood to flow from the atria to the ventricles.

A semilunar valve is a valve that allows blood to flow from the ventricles to the arteries.

During atrial systole, the walls of the atria contract, decreasing atrial volume and increasing atrial pressure.

Ventricular systole is the contraction of the walls of the ventricles, decreasing ventricular volume and increasing ventricular pressure.

During atrial systole the AV valves are open and the semilunar valves are closed.

During ventricular systole the AV valves are closed and the semilunar valves are open.

During diastole the AV valves are open and the semilunar valves are closed.

False.

Osmosis must take place across a cell membrane, therefore water moving through the xylem does not move by osmosis. Water also moves by diffusion as well as due to pressure.

Root pressure is the positive pressure generated in the xylem by the entry of water from the roots, which helps to push water up the stem of the plant.

The purpose of root pressure is to drive the movement of water up xylem vessels when the rate of transpiration is low.

True.

Transpiration creates a negative pressure inside xylem vessels.

True.

Root pressure is important in driving the movement of water up xylem vessels when the rate of transpiration is low.

False.

Translocation describes the transport of organic compounds in the phloem tissue.

Phloem sap is the liquid that is being transported within the phloem, consisting of sugars in the form of sucrose, along with water and other dissolved substances such as amino acids.

Sources are the regions of plants in which organic solutes originate, such as mature green leaves, green stems, and storage organs.

A sink is a region of the plant where organic compounds are required for growth, such as meristems, growing roots, and developing seeds or fruits.

The two main cell types in phloem tissue are sieve tube elements and companion cells.

Sieve plates allow the passage of assimilates between sieve tube cells, facilitating the continuous movement of organic compounds.

Plasmodesmata are bridges of cytoplasm that link companion cells and sieve tube elements, allowing assimilates to move between them.

The active loading of sucrose into the phloem at the source lowers the water potential, causing water to move into the phloem vessels by osmosis, which generates a hydrostatic pressure gradient for the translocation of organic compounds.

Hydrostatic pressure refers to the pressure exerted by a fluid on the walls of its container, in this case, the walls of the phloem.

Mass flow is the process by which the contents of the phloem, including organic compounds, flow from the source to the sink down a hydrostatic pressure gradient.