Biology Quiz: Plant Transpiration and Heart Function

Blood Vessels

• The circulatory system contains various types of blood vessels: arteries, arterioles, capillaries, venules, and veins.
• Each blood vessel type has a specific structure related to its function.

Capillaries

• Capillaries are the exchange surface in body tissues.
• Their walls are one cell thick (endothelial cells), minimizing diffusion distance for substances like oxygen and carbon dioxide.
• Some capillaries have gaps (fenestrations) allowing plasma to leak out, forming tissue fluid.

Arteries

• Arteries carry blood away from the heart at high pressure.
• Their walls have three layers: an inner endothelium (smooth for reduced friction), a middle layer of thick smooth muscle and elastic tissue.
• Elastic tissue helps maintain pressure, while smooth muscle regulates blood flow and pressure.
• Arteries have a narrow lumen compared to their thickness to maintain high pressure.

Veins

• Veins carry blood back to the heart at low pressure.
• Their walls have thinner smooth muscle and elastic tissue compared to arteries enabling vessels to be more compliant.
• Veins have a wider lumen compared to their thickness to maximize blood flow.
• Veins have valves to prevent backflow of blood.

Measuring Pulse Rate

• Pulse rate can be measured by placing two fingers on the radial or carotid artery.
• Count the number of pulses felt for 60 seconds.
• Alternatively, count for 30 seconds and multiply by 2.
• Do not use your thumb to take a pulse.

Coronary Heart Disease

• Coronary heart disease results from the narrowing of the coronary arteries due to a blockage.
• This blockage can be caused by atherosclerosis, where fatty deposits (atheromas) build up under the endothelium.
• Atherosclerosis is often the result of high blood pressure.

Evaluating Epidemiological Data

• Claims about lifestyle risk factors and heart disease are often based on correlation, not causation.
• Epidemiological studies examine large populations, but these studies cannot determine cause-and-effect.
• Results must be statistically significant, and must be able to be replicated in controlled studies and with broader populations.

The Transpiration Stream

• Water evaporates from leaves during transpiration, creating a negative pressure in the xylem.
• This pull is transmitted through the plant due to cohesion between water molecules.
• This process is sometimes called the cohesion-tension theory.

Adaptations of Xylem Vessels

• Xylem vessels are long, continuous, hollow tubes.
• They have thickened walls (cellulose and lignin) to withstand tension.
• Pits in the walls allow water to move sideways between vessels.

Dicotyledonous Stem Structure

• The stem has several tissues including the epidermis (outer layer), cortex (beneath the epidermis), and pith (central region).
• Vascular tissue is arranged in a ring of vascular bundles.
• Dicotyledonous stems have different types of tissues including the vascular bundles or the xylem and phloem arranged in a ring, the cortex, and the pith.
• Plan diagrams should not contain shading, and should include annotations giving functions.

Dicotyledonous Root Structure

• Xylem is centrally located in the root, in a cross-shaped structure.
• Phloem tissue is located between the cross "arms" of the xylem.
• The cortex and epidermis are regions for storage and protection.

Tissue Fluid

• Plasma filters out of the capillaries at the arterial end, forming tissue fluid.
• Tissue fluid surrounds body cells for exchange of materials.
• The proteins and cells in the blood are too large to leave the capillaries and remain in the blood.
• Pressure filtration and reuptake of fluid balance formation of tissue fluid.
• At the venous end most of the fluid re-enters the capillaries via osmosis and pressure differences.

Circulatory Systems (HL)

• Bony fish have single circulation (blood passes through the heart once).
• Mammals have double circulation (blood passes through the heart twice).
• Double circulation allows a higher blood pressure and helps to keep oxygenated and deoxygenated blood separate.

The Mammalian Heart

• The four-chambered heart has two atria and two ventricles to separate oxygenated and deoxygenated blood.
• Valves ensure unidirectional blood flow.
• The Sinoatrial node (SAN) is the pacemaker and initiates the heartbeat, coordinating contraction.

The Cardiac Cycle

• The cardiac cycle consists of atrial systole, ventricular systole, and diastole.
• The wave of depolarisation spreads across the heart in a coordinated manner (contraction or relaxation of the chambers).
• Pressure and volume changes drive the opening and closing of valves during the cycle.

Coronary Arteries

• Coronary arteries supply the heart muscle with oxygenated blood.
• These arteries have branched to the heart muscle.

The Roots and Water Transport

• Transpiration creates a negative pressure in the xylem, pulling water up the plant.
• Root pressure can also help move water upwards, especially in conditions where transpiration is low
• The movement of water can be due to the action of the root cells or due to the evaporative pull within plant leaves

Translocation in Plants

• Translocation is the movement of organic substances in the phloem (organic compounds or assimilates).
• Sources are regions producing organic compounds (sugars), such as mature leaves, whereas sinks are regions that use compounds (such as growing tissues).
• The movement of organic compounds through the phloem is an active process, facilitated by the high hydrostatic pressure at the source and the low hydrostatic pressure at the sink.
• Sieve tube cells and companion cells are crucial components of phloem tissue facilitating translocation.