Biology 2.13


A level Biology (Unit 2) Note on Biology 2.13, created by Olivia22 on 12/04/2013.
Note by Olivia22, updated more than 1 year ago
Created by Olivia22 about 11 years ago

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InsectsWaterproofing 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. 

FishGills 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.

LeavesThin,flat shape with large surface area. Diffusion takes place in the gas phase(air) which is rapidMany 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 liverHepatic vein - liverRenal vein - kidney

ArteryThick muscle layercan be constricted and dilatedThick elastic layerMaintain high blood pressure with recoil actionThick wallresists bursting with high pressureNo valvesconstant high pressure

VeinThin muscle layerconstriction and dilation no control of bloodThin elastic layerpressure too low for recoil actionThin wallpressure too low for any burstingValves throughoutprevent back flow 


Only lining layersmall distance for diffusionNumerous and branchedlarge surface areaNarrow diameterno cell is far from one

Narrow lumenred blood cells squeezed throughSpaces between endothelial cellsallow white blood cells to escape


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

Movement of water up stemsCohesion-Tension theoryWater 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 pullCauses 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.

TranspirationLight - 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 holdHumidity - affects the water potential gradient between the air inside the leaf and outside the leafAir movement - reduces water potential of the air as it prevents accumulation of water around the stomata

XerophytesThick cuticlereduce water lost through cuticleRolled leavestraps a region of still airno water potential gradient hairs on leavestraps a region of still air around stomata water potential gradient is reducedStomata in pits/groovestraps moist airreduce water potential  gradientreduced surface area to volume ratiorate of water loss reduced

Gas Exchange

Circulatory system

Water in plants

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