organisation: plant tissues, organs and systems

aqa triple higher

tissue

a group of similar cells that work together to perform a particular function

organ

a group of different tissues that work together to perform a particular function

function of the flower

pollination (gametes fuse to produce seeds)

function of the leaf

photosynthesis

function of the bud

develops into a flower, has meristems

function of the stem

transport (e.g. xylem, phloem) and structure, holds up leaves to sun to maximise photosynthesis

function of the roots

absorb nutrients, mineral ions (by active transport) and water (by osmosis) through root hair cells, anchor plant in the ground

how are leaves adapted for gas exchange?

wide and flat - large SA, short diffusion distance, faster gas exchange/thin so gases can reach cells easily/air spaces allow gases to diffuse easily to all cells/lots of stomata through which gases move in and out

how are roots adapted?

long and thin - large SA, short diffusion distance, faster root uptake/long and thin - large SA so good at absorbing water, have a semi permeable membrane for osmosis, short distance from xylem which carries water to the rest of the plant/contain lots of mitochondria which release energy for active transport, lots of carrier proteins in cell membranes

stomata in the day and why

• take in water by osmosis, becomes turgid, stomata open

• this is to allow for greater gas exchange for photosynthesis

stomata at night and why

• lose water by osmosis, becomes flaccid, stomata close

• to prevent water loss when no photosynthesis is occurring as no CO2 is needed

transpiration

loss of water vapour from the shoot/leaf system of a plant by evaporation

transpiration stream

movement of water through a plant from the roots to the leaves

why is transpiration important for a plant?

carries water to leaves for photosynthesis and to keep cells turgid/carries minerals to leaves for protein synthesis/cools the plant in hot weather

environmental factors that increase the rate of transpiration

hot, dry, windy

environmental factors that decrease the rate of transpiration

cold, humid, still

how does high temperature affect the rate of transpiration?

• kinetic energy of water particles increases

• rate of osmosis out of leaf increases

• so concentration gradient increases

• so rate of transpiration increases

how does wind/air movement affect the rate of transpiration?

• kinetic energy of water molecules increases

• moving water molecules away

• rate of osmosis out of leaf increases

• so concentration gradient increases

• so rate of transpiration increases

how are xylem adapted for transpiration?

long continuous tubes so water can move through easily/contain lignin which allows it to withstand pressure changes as water moves throughout the plant/no organelles or cytoplasm so more space for water

translocation

movement of food molecules (such as sucrose) through phloem tissue (up and down the plant)

what is translocation needed for?

growing parts of the plant for immediate use/storage organs/developing seeds

how is the phloem adapted for translocation?

sieve tubes - each have a perforated end so cytoplasm connects them together/companion cells - connect to sieve tubes to release energy

compare the structure and function of the xylem and phloem

• xylem consists of dead cells, phloem consists of alive cells

• xylem transports water during transpiration, phloem transports sucrose during translocation

• phloem transports substances in both directions but xylem only transports substances upwards

• translocation in the phloem requires energy but transpiration in the xylem is a physical process so does not require energy

what is this part of the leaf called and what is its function?

palisade mesophyll tissue - contains lots of chloroplasts which contain chlorophyll for photosynthesis and the enzymes needed for photosynthesis

what is this part of the leaf called and what is its function?

upper epidermis - transparent so light can pass through to the palisade layer for photosynthesis

what is this part of the leaf called and what is its function?

spongy mesophyll tissue - contain large air spaces to increase the SA:V and therefore rate of diffusion of gases such as O2 and CO2 in and out of the leaf

what is this part of the leaf called and what is its function?

lower epidermis - contain lots of stomata and guard cells so CO2 can diffuse into the leaf and O2/water can diffuse/osmose out of the leaf

where is the waxy cuticle and what is its function?

• situated at the top and bottom of the leaf

• reduces water loss

what are the roles of the stomata?

to control gas exchange and water loss

how does high humidity affect the rate of transpiration?

• decreases rate of transpiration

• the drier the air around the leaf, the higher the rate of transpiration

• humid air causes conc gradient of water between air and leaf to decrease

• so rate of osmosis out of leaf decreases

how does high light intensity affect the rate of transpiration?

• increases rate of photosynthesis

• so stomata open

• so water osmoses out of leaf

how are root hair cells adapted for their function?

• large SA:V to increase rate of osmosis/active transport of water/mineral ions and provide contact with soil water

• thin walls so as not to restrict movement of water

(not required) how could a student investigate factors affecting transpiration?

measure change in mass over time:

• air movement - direct fan on leaves

• temperature - heater

• obstructing stomata - e.g. using petroleum jelly

• light intensity - artificial lighting

(not required) how could a student investigate the rate of transpiration?

using a potometer:

• fill w water

• cut shoot underwater and insert into rubber tubing

• raise potometer so air bubble is taken up

• lower back into water and record distance travelled over a period of time

• repeat

• plot graph excluding any anomalies

(not required) how could a student investigate the distribution of stomata and guard cells?

• paint surface of leaf a clear nail varnish

• wait to dry

• peel off w forceps

• place on dry microscope slide and examine

• calculate density of stomata per unit area