Sixth Year Biology Transport, Storage and Gas Exchange in Flowering Plants Miss Rochford
In this topic: Uptake and transport of: Water and minerals Carbon dioxide Gas exchange Transport of photosynthesis products Modified food storage organs
Why do plants need a transport system? For photosynthesis and other metabolic processes, plants need: Water Carbon Dioxide Oxygen Minerals Nutrients These need to be transported within the plant
UPTAKE AND TRANSPORT OF MATERIALS IN PLANTS
Root hairs and absorption Root hairs have many adaptations for absorption Thin walls Not covered by a cuticle Large surface area by being numerous
Osmosis
Root hairs and absorption Cytoplasm in root hair: Lots of dissolved materials Soil water: Less concentrated than root hair cells Water moves by osmosis into the root hair cells
Movement of Water into Xylem How does this happen? DIFFUSION Water moves from: To: Method Root hairs Ground tissue Diffusion Ground tissue Xylem Diffusion
Movement of Water into Xylem
Upward Movement of Water Two mechanisms involved: 1. Root Pressure 2. Transpiration
Root Pressure Build-up of water in roots causes a rise in pressure This pressure pushes water up through the xylem BUT, it s not strong enough on its own. It works together with transpiration
Root Pressure: Guttation
Transpiration Transpiration: the loss of water vapour from the aerial parts of a plant Helps to keep water moving upwards through the plant Water exits through stomata Stomata: openings on the underside of leaves
Transverse Section of a Leaf (Learn labels)
Control of transpiration Control Explanation Waxy cuticle on leaves Prevents excess water loss Stomata positioned underneath leaves Stomata can open and close Lower rate of evaporation here This can reduce water loss when needed
Mineral uptake and transport Plants need minerals such as: Calcium Magnesium Nitrates Phosphates Sodium Potassium
Mineral uptake and transport Diffusion Some minerals absorbed this way Does not require energy Also known as passive transport Active Transport Some minerals are absorbed by active transport This requires energy
Uptake and transport of CO 2 1. Atmospheric Carbon Dioxide Enters through stomata Diffuses into photosynthesising cells in ground tissue 2. Carbon Dioxide from Respiration Respiration in the mitochondria of the leaf produces CO 2 This is also used for photosynthesis
Fate of products of photosynthesis Oxygen Diffuses into air spaces in the leaf Some used in respiration The rest is diffused out of stomata
Fate of products of photosynthesis Glucose Three possibilities: 1. Used immediately for Respiration 2. Stored as starch 3. Converted to sucrose and transported through phloem as phloem sap
COHESION-TENSION THEORY
Amazing water transport in trees
Cohesion-Tension Model Cohesion: the sticking of similar molecules to each other Water has high cohesion Adhesion: occurs when different molecules stick together Water adheres to the walls of xylem Water s cohesive force is greater than its adhesion to xylem
Cohesion-Tension Model 1. Transpiration involves water leaving through stomata Each water molecule pulls the next due to their high cohesion 2. This pulling of the water means that the water in xylem is under tension 3. Water can be pulled up to 150 m
Night Day
Cohesion-Tension Model
FOOD STORAGE IN PLANTS
Food storage organs in plants Formed from Tap Roots Modified roots are swollen with food stores Examples: Carrot Parsnip Turnips Modified Root
Food storage organs in plants Modified Stem Stems swell to form a food store Potatoes are underground stems, swollen with starch Another example = asparagus
Modified Leaves
Food storage organs in plants Modified Leaves Bulbs: a reduced stem and modified leaves Leaves are swollen and fleshy to store food Central apical bud is within the leaves Bulb is protected by dry scaly leaves
GAS EXCHANGE
Gas exchange in the leaf Carbon Dioxide CO 2 is needed for photosynthesis It diffuses into leaves through stomata It diffuses to the ground tissue through air spaces between cells Air spaces increase surface area of the leaf
Gas exchange in the leaf Oxygen Oxygen diffuses from the ground tissue into the air spaces It exits through stomata Water vapour Water vapour diffuses out through the stomata The process is known as TRANSPIRATION
Gas Exchange in Stems Lenticels: small pores on a stem that function in gas exchange
Stomatal opening and closing (HL) Generally: Time Stomata Reason Day Open Gas exchange for photosynthesis Night Closed Help reduce loss of water when gas exchange is not necessary
Stomatal opening and closing (HL) Environmental conditions can also cause stomata to close Condition Windy weather Calm conditions High temp Behaviour of stomata Wind increases transpiration rate Stomata close to minimise water loss Stomata open Stomata close to preserve water
Stomatal opening and closing (HL) Guard cells control stomatal opening and closing by controlling their turgidity
Turgid guard cells Swollen with water Curve away from each other Stoma are open Flaccid guard cells They have lost water Cells are close together Stoma are closed
Chapter 25: Transport, Storage and Gas Exchange in Flowering Plants DONE!!