B3.2 Transport

What is the role of arteries?

arteries carry blood leaving heart;

How is the structure of arteries related to their function?

so have thick walls to withstand high pressure; arteries have 3 major layers:

• tunica externa — a tough outer layer of connective tissue with collagen fibres

• tunica media — a thick layer containing smooth muscle and elastic fibres made of the protein elastin

• tunica intima — a smooth endothelium forming the lining of the artery; in some arteries the tunica intima also includes a layer of elastic fibres

How is arterial pressure maintained by arteries?

The muscle and elastic fibres assist in maintaining blood pressure between pump cycles

• circular muscles in the arteries can contract in vasoconstriction

  • Increasing blood pressure

• When the heart contracts during systole, elastic fibres stretch storing potential energy

• During relaxation of the heart elastic fibres recoil; increasing blood pressure;

What is the role of capillaries?

Blood flows through tissues in capillaries with permeable walls; that allow exchange of materials between cells in the tissue and the blood in the capillary;

What is the role of veins?

Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart;

How is the structure of veins related to their function?

veins have thinner walls relative to their widths; a wider lumen relative to their width; far fewer elastic tissues and muscle than arteries; as they are low pressure, veins have valves to prevent backflow of blood; to maintain one

Name a device used for measuring the rate of water uptake of a plant due to photosynthesis and transpiration.

Potometer

Name the force created by evaporation of water coupled with the cohesive and adhesive forces in plants, enough to support a column of water against the forces of gravity in plants and trees.

Water tension

Define Transpiration

the loss of water by evaporation in terrestrial plants, especially through the stomata (accompanied by a corresponding water uptake from the roots).

Name the woody tissue which supports and transport water in vascular plants.

Xylem

Explain why transpiration is the inevitable (must happen) consequence of gas exchange

• Plants must take in carbon dioxide from the atmosphere for photosynthesis;

• they must release oxygen as a waste product of photosynthesis

• exchange of these gases must take place to sustain the plant

• waxy cuticle is not very permeable, so gases cannot be exchanged through it, therefore must happen through stomata

• most plants grow in areas where humidity (water content of air) is lower than in their leaves

• therefore, if the stomata (pores in the leaves) are open, water will leave the leaf during daytime by evaporation from the the spongy mesophyll and airspaces, through the guard cells down water potential gradient

Explain how the structure of xylem helps it to withstand low pressure and why this is important

Long continuous tubes; thick walls which are impregnated (contain) lignin; lignin is strong and water

Explain how tension in the leaf and evaporation maintain the transpiration stream

water evaporates from the cell walls (surface) of cells in the air spaces of leaves (spongy mesophyll); this causes water to be drawn from the nearest source; which is xylem; due to adhesion of water molecules; therefore pulling the whole continuous stream of water molecules towards the leaf; from the roots; this is called transpiration

Explain how tension is generated in the xylem (in leaves).

loss of water by transpiration from cell walls in leaf cells causes water to be drawn out of xylem vessels and through cell walls by capillary action, beacause of water is cohesive this generates tension (negative pressure potentials) pulling water up to replace the lost water.

Phloem

food-conducting tissue of vascular plants that conducts synthesized nutrients to different parts of the plants.

What structural feature of capillaries maximizes their surface area for material exchange?

Branching into a large network of narrow vessels.

Why do capillaries have thin walls?

To allow efficient diffusion of gases, nutrients, and waste.

What are fenestrations in capillaries, and why are they important?

Small pores that enable rapid exchange of substances like proteins and hormones.

How can you distinguish an artery from a vein in a micrograph?

Arteries have thicker walls and a smaller lumen, while veins have thinner walls and a larger lumen.

Why do arteries have thick walls compared to veins?

To withstand the high pressure of blood pumped from the heart.

Why do xylem vessels lack cell contents and have incomplete end walls?

To allow unimpeded flow of water through the vessels.

What role do lignified walls in xylem vessels play?

They provide structural support and withstand the tension created by water transport.

What is the primary function of the cortex in the stem of a dicotyledonous plant?

To store nutrients and provide support.

What is the function of the epidermis in the root of a dicotyledonous plant?

To protect the root and facilitate water absorption.

Compare and contrast tissue distribution in a transverse section of the stem and root of a dicotyledonous plant.

In the stem, vascular bundles are arranged in a ring, whereas in the root, the vascular bundles are centrally located with a star