Biology 2.13

Page 1

Insects

Waterproofing over body surfaces. Rigid outer skeleton and a waterproof cuticle over it.

Small surface area to volume ratio. Minimise area water is lost.

Gases move into trachea and tracheoles down concentration gradient.

Movement of muscles creates mass movement of air in and out of tracheae. This ventilation speeds up gas exchange.

Spiracles are pores on the body surface.They are opened and closed by a valve.

Fish

Gills made of gill filaments stacked up in a pile.

Gill filament contains many gill lamellae on it at right angles to the filament.

Water flows in the opposite direction to the blood flow (countercurrent flow).

This means that there is always a constant concentration gradient.

Leaves

Thin,flat shape with large surface area.

Diffusion takes place in the gas phase(air) which is rapid

Many stomata (pores) in lower epidermis mostly, stomata can open and close.

Features of a transport system

A suitable medium for transport

A form of mass transport

A closed system of tubular vessels

A mechanism for moving transport medium within vessels

A mechanism to maintain mass flow movement

A means of controlling flow

Hepatic portal vein - stomach to liver

Hepatic vein - liver

Renal vein - kidney

Artery

Thick muscle layer

can be constricted and dilated

Thick elastic layer

Maintain high blood pressure with recoil action

Thick wall

resists bursting with high pressure

No valves

constant high pressure

Vein

Thin muscle layer

constriction and dilation no control of blood

Thin elastic layer

pressure too low for recoil action

Thin wall

pressure too low for any bursting

Valves throughout

prevent back flow

Capillary

Only lining layer

small distance for diffusion

Numerous and branched

large surface area

Narrow diameter

no cell is far from one

Narrow lumen

red blood cells squeezed through

Spaces between endothelial cells

allow white blood cells to escape

Capillary

Tissue-fluid

-at arteriole end of capillary hydrostatic pressure is high and forces water and molecules out of capillary

-hydrostatic pressure decreases and osmotic pressure is greater , osmosis causes water to re-enter the capillary at the venule end of the capillary

-excess tissue fluid is returned to the circulatory system via the lymphatic system.

Movement of water through roots

Apoplastic pathway

When water is drawn in from roots it can travel from cell to cell via the cellulose cell walls due to its cohesive properties. Casparian strips are found in the cell walls to prevent this and force water into cytoplasm.

Symplastic pathway

Water can also move via the cytoplasm of each cell by osmosis , passing through plasmodesma to reach a new cell

Movement of water up stems

Cohesion-Tension theory

Water evaporates off leaves in transpiration.

Due to cohesion water molecules stick together and form a continuous pathway across mesophyll cells. Molecules of water are drawn up the stem due to evaporation of water - transpiration pull

Causes diameter of trunks to decrease during the day due to more tension . If air enters, water cannot be drawn up. Also water does not leak out as it is under tension.

Transpiration

Light - stomata open in the light as photosynthesis is occurring

Temperature - increases kinetic energy/speed of water molecules and the amount of water that the air can hold

Humidity - affects the water potential gradient between the air inside the leaf and outside the leaf

Air movement - reduces water potential of the air as it prevents accumulation of water around the stomata

Xerophytes

Thick cuticle

reduce water lost through cuticle

Rolled leaves

traps a region of still air

no water potential gradient

hairs on leaves

traps a region of still air around stomata

water potential gradient is reduced

Stomata in pits/grooves

traps moist air

reduce water potential gradient

reduced surface area to volume ratio

rate of water loss reduced

Gas Exchange

Circulatory system

Water in plants