Biology 12

Plant transport systems

Forces acting on transport

Forces in the leaves Transpiration – water lost from leaves Evapo-transpiration – water lost from leaves as water evaporates Transpiration stream – water is pulled up the stem as water is lost from the leaves in transpiration

Forces in the stems Adhesion – water molecules stick to the sides of the walls in the xylem Cohesion – water molecules stick to each other Capillarity/capillary action – water is drawn upwards through thin tubes

Forces in the roots Active transport – salts are actively absorbed, increasing the osmotic pressure within the roots Osmosis – water is pulled in due to the concentration gradients

Translocation

Movement of sugar Translocation – movement of sugar – sugar is actively transported from leaf to phloem (source) and from phloem to roots (sink), thus setting up a concentration gradient from leaf to roots Diffusion – sugar will diffuse downwards because of this concentration gradient Osmosis – water will be pulled out of the xylem near the leaves, and move downwards, then return to the xylem near the roots, due to the concentration gradient.

Plant transport systems Roles of Leaves – carry out photosynthesis and transpiration Stomata – allow water and gases to enter and leave the leaf. Opening is controlled by guard cells Xylem – transports water and salts upwards Phloem – transports sugars, mostly downward Roots – draw in water and salts Root hairs – increase surface area

Leaves and stomata 1

Leaves and stomata 2 Leaves are responsible for photosynthesis and exchange of gases and water Gases and water enter and leave through the stomata Epidermis provides protection Palisade cells carry out photosynthesis The spongy mesophyll layer allows storage of air and water vapour Vascular bundles contain xylem and phloem for the transport of water, salts and sugars

Control of stomal opening

Control of stomal opening 2 Stomatal opening is controlled by turgor pressure in the guard cells This is controlled by pumping salts into the cells, thus bringing in more water (opening stoma) or pumping salts out of the cells, thus forcing water to leave (closing stoma) Turgor pressure increases when water availability is high Turgor pressure decreases when water availability is low

Structures in the stem

Xylem and phloem XylemPhloem Cells living/dead DeadLiving Cell walls: Thickness Material Permeability Thick Lignin Impermeable Thin Cellulose Permeable Cross walls NoneSieve plates Cytoplasm NoneYes Function Carries water & saltsCarries sugars Direction of flow UpwardsDown and up Special features FibresCompanion cells

Roots and water transport Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman

Root hairs and water transport Water moves in by osmosis Osmotic pressure in root hair cell is higher than in soil This can be maintained by active transport of salts into the root hairs Root hairs increase the surface area available

Measuring water loss This can be done with a device called a potometer The rate of transpiration is shown by movement of a bubble of air through the tubing Key features include – air tight seal between plant and tubing, narrow tubing, intact stem (cut under water so it will draw up water), air bubble, scale

Water loss in plants Factors affecting water loss Temperature Humidity Air movement Water availability Light intensity Decreasing water loss also decreases p

Water balance – freshwater fish Problems: Solutions: Produces urine Does not drink Eats Gills Kidneys

Water balance – marine fish Problems: Solutions: Produces urine Constantly Gills Kidneys

Water loss in animals - rats Which rat would need to drink more? What differences would you expect in their kidneys? Kangaroo ratLab rat Input - barley54 mL Output – urine faeces evaporation 13.5 mL 2.5 mL 44 mL 22 mL 13.6 mL 77 mL Deficit

Arid Namebody (kg)RMTkidney (g)habitatRMT/bodykidney/body M niata D A cinererea D C lanigera D O glyroides D O degus D X inauris D D merriami D D microps D C penicillatus D J jaculus D A olivaceus D Abrothrix andinus D A andinus D B lacteris SD A varius SD A berlepschii D A albiventer SD C callosus SD C musculinus SD E puerulus D E typus SD E hirtipes D E marica SD G griseoflavus SD G domorum D A edax D A sublimis D Averages Rodents from arid regions

Wet Namebody (kg)RMTkidney (g)habitatRMT/bodykidney/body D leporina M A bennetti M O bridgesi M O lunatus M A fuscus M A sagei M S cyanus M F pennanti M S beecheyi M C ludovicianus M C leucurus M N ebriosus M O longicauditas M A xanthorhinus M A longipilis M C macronyx M C lepidus M L pikumche M P leucopus M M agretis M C cricetus M R norvegicus M M musculus M O angioniensis M O irroratus M O s robertsi M Rodents from wet regions

Kidney adaptations- averages AridWet Relative Medullary Thickness (RMT) Kidney mass (g) Body mass (g) RMT:body mass Kidney:body mass General trends – animals from arid regions have comparatively larger kidneys, with thicker medullas than those from wetter areas – this allows these animals to reabsorb more water

Kidney adaptations 2 General trends – animals from arid regions have comparatively larger kidneys, with thicker medullas than those from wetter areas – this allows these animals to reabsorb more water

Multiple choice questions 1. Which of the following is an inference? (a) Commercial timber produced from older trees is denser than timber from young trees of the same species. (b) The outer layer of sapwood of a tree is often a different colour from the inside of the trunk. (c) Areas of forest that currently produce the best timber will remain the best areas for future timber production. (d) The timber of some species of tree is unsuitable for commercial use. 2. A bird in a cold environment can reduce heat loss by which of the following processes? (a) Panting (b) Flying vigorously (c) Increasing its metabolic rate (d) Erecting its feathers

Multiple choice questions 1. Which of the following is an inference? (a) Commercial timber produced from older trees is denser than timber from young trees of the same species. (b) The outer layer of sapwood of a tree is often a different colour from the inside of the trunk. (c) Areas of forest that currently produce the best timber will remain the best areas for future timber production. (d) The timber of some species of tree is unsuitable for commercial use. 2. A bird in a cold environment can reduce heat loss by which of the following processes? (a) Panting (b) Flying vigorously (c) Increasing its metabolic rate (d) Erecting its feathers

Multiple choice questions 2 3. Which statement about photosynthesis is correct? (a) The rates of photosynthesis and respiration are equal at all times in plants. (b) The overall chemical change in photosynthesis is the opposite of aerobic respiration. (c) The part of the photosynthesis reaction that does not involve oxygen occurs in the cytoplasm. (d)Photosynthesis occurs in the mitochondria. 4. Which of the following statements about enzymes is most correct? (a) Enzymes are usually specific for a particular substrate. (b) Enzymes are used up in the chemical reactions they catalyse. (c) Enzymes usually catalyse many different chemical reactions. (d) Enzymes decrease and increase the rates of chemical reactions.

Multiple choice questions 2 3. Which statement about photosynthesis is correct? (a) The rates of photosynthesis and respiration are equal at all times in plants. (b) The overall chemical change in photosynthesis is the opposite of aerobic respiration. (c) The part of the photosynthesis reaction that does not involve oxygen occurs in the cytoplasm. (d)Photosynthesis occurs in the mitochondria. 4. Which of the following statements about enzymes is most correct? (a) Enzymes are usually specific for a particular substrate. (b) Enzymes are used up in the chemical reactions they catalyse. (c) Enzymes usually catalyse many different chemical reactions. (d) Enzymes decrease and increase the rates of chemical reactions.

Multiple choice questions 3 5. You have a freshwater aquarium at home and have just purchased a new fish. To your dismay, the fish dies within a day of placing it in your tank. You later discover that it was a marine fish. Select the best explanation of the fish's death. (a) The fish gained too many salts by active transport across its gills. (b) The fish produced too much urine. (c) The fish gained too much water through its body surface. (d)The fish drank too much fresh water. 6. Which of the following statements about the way endothermic animals regulate their body temperature is NOT correct? (a) The metabolic rate decreases during periods of inactivity. (b) The metabolic rate decreases in warm conditions. (c) The metabolic rate increases in cool conditions. (d) The metabolic rate increases during periods of activity

Multiple choice questions 3 5. You have a freshwater aquarium at home and have just purchased a new fish. To your dismay, the fish dies within a day of placing it in your tank. You later discover that it was a marine fish. Select the best explanation of the fish's death. (a) The fish gained too many salts by active transport across its gills. (b) The fish produced too much urine. (c) The fish gained too much water through its body surface. (d)The fish drank too much fresh water. 6. Which of the following statements about the way endothermic animals regulate their body temperature is NOT correct? (a) The metabolic rate decreases during periods of inactivity. (b) The metabolic rate decreases in warm conditions. (c) The metabolic rate increases in cool conditions. (d) The metabolic rate increases during periods of activity