transpiration

which species predominate in agricultural systems

crop species selected by farmers

what is the impact of agriculture on the gene pool

crop species have been selectively bred over generations for desirable characteristics, so variety of alleles has been reduced

what is the effect of chemicals on crops

increases yield and therefore profit, herbicides used to remove weeds (as theres competition for crop resources) and pesticides used to remove pests (which cause drop damage). this causes low species diversity

what are some farming practises that have reduced biodiversity (7)

removal of hedgerows, monoculture, infilling ponds and draining wetlands, overgrazing land, use of chemicals, effluent run-off into water courses, lack of crop-rotation

what is the effect of hedgerow removals on biodiversity

makes planting, treating and harvesting of crops more efficient, however causes habitat loss therefore reducing biodiversity

what is the effect of monoculture on biodiversity

more efficient to grow just one crop however reduces species diversity

what is the effect of infilling ponds and draining wetlands on biodiversity

reduces biodiversity due to habitat loss

what is the effect of overgrazing land on biodiversity

maximising livestock yield but can irreparably damage the soil, leading to reduced plant diversity

what is the effect of the se of chemicals- pesticides, herbicides, inorganic fertilisers, on biodiversity?

maximises productivity but reduces the number of species

what is the effect of effluent run-off into water courses on biodiversity

causes eutrophication

what is the effect of lack of crop rotation on biodiversity

will deplete certain soil nutrients, leading to reduced biodiversity

how does water travel from the xylem, through the tissues and out of the leaf?

water evaporates from spongy cells, making the air spaces humid. this lowers the water potential of the spongy cells and water moves into them from the xylem by osmosis. air outside the leaf is less humid so water vapour diffuses down the concentration gradient and out through the stomata.

how could a potometer be used to measure the effect of a given environmental factor on the rate of water uptake by a leafy shoot?

measure the distance the bubble moves in mm in a given time. calculate volume of water taken up using radius of capillary tube: pi r squared h. (h is distance moved). reset bubble using tap to release water from the reservoir. repeat and calculate mean value.

cohesion tension theory

in leaf, water moves by osmosis from xylem vessels to mesophyll cells. this creates negative pressure in leaf xylem vessels which pulls other water molecules up from the stem xylem. hydrogen bonds between water molecules maintain an unbroken column of water due to cohesion. column of water pulled up plant due to evaporation from leaf- transpiration pull. water from the soil enters the roots and moves by osmosis into xylem to replace what is drawn up by transpiration pull

tree diameter varies during day and night. when is tree diameter lowest?

diameter decreases during the day because xylem is under negative pressure so xylem vessels are slightly thinner than at night when transpiration reduces

if a xylem vessel breaks and air enters, the tree can no longer draw up water. why not?

if the water column is broken, cohesion is lost between water molecules and thus negative pressure is lost

when a xylem vessel breaks, water doesnt ooze out as it would in a blood vessel for example. instead, air is drawn in. what does this prove?

that water in the xylem is under negative pressure