[BIO] Chapter 5 - Nutrition in Plants

© Hee Xin Wei (Copyrighted) Topic 5: Nutrition in Plants

Chapter Analysis FOCUS EXAM WEIGHTAGE © Hee Xin Wei (Copyrighted) •straightforward chapter •link structure of leaf and photosynthesis knowledge from this chapter to the next •Constitute to around 6% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions

Leaf Structure Gaseous exchange Key Concept © Hee Xin Wei (Copyrighted)

Structure of Leaf Tissue Structure & Functions Chloroplast distribution Cuticle •Waxy and transparent layer. •Reduced water loss through evaporation from the leaf No Upper epidermis •Single layer of closely packed cells •Allows light to pass through. No Palisade Mesophyll •Long and cylindrical shape •Main site of photosynthesis Contain the largest amount of chloroplasts among the tissue in leaves to increase absorption of sunlight for photosynthesis Spongy Mesophyll •Irregular shape with large intercellular air spaces among the cells to increase surface area for gaseous exchange. •covered with a thin film of moisture so that carbon dioxide can dissolve in it. •Contains vascular bundle. Contain less chloroplasts than palisade mesophyll © Hee Xin Wei (Copyrighted)

Structure of Leaf Tissue Structure & Functions Chloroplast distribution Vascular Bundle •containing xylem and phloem tissue •Xylem: transport water and mineral salts from roots to other part of plants •Phloem: transport sucrose from leaves to other parts of plants No Intercellular air spaces •The intercellular air spaces in the spongy mesophyll allow circulation of Carbon Dioxide and Oxygen inside leaf for photosynthesis and respiration •rapid diffusion of gases into and out of the cells No Lower Epidermis •Similar to upper epidermis, a single layer of closely-packed cells covered by cuticle No (but the layer of tissue consists of guard cells which contain chloroplast) Guard cells •Guard cells are bean-shaped cells that surround stoma •guard cells have a thicker cellulose cell wall on the side of stomata •Control the opening and closing of the stoma that allow gaseous exchange of leaves Yes © Hee Xin Wei (Copyrighted)

Gaseous Exchange -Plants open their stomata during the day for carbon dioxide intake and close their stomata during the night to minimise water loss through transpiration. During the day •Guard cells photosynthesise and energy is used to pump potassium ions by active transport into the guard cells from neighbouring epidermal cells. •This lowers the water potential of guard cells •Water from neighbouring cells enter guard cells via osmosis •Guard cells swell and become turgid. Due to uneven thickness of cell walls, guard cells become curved and lead to the opening of stoma In the night •Potassium ions move out of the guard cells via diffusion •Water potential is increased in guard cells •Water moves out of the guard cells to the neighbouring cells •Guard cells become flaccid and the stoma closes. Guard cells and stomata © Hee Xin Wei (Copyrighted)

Photosynthesis Limiting Factors Key Concept © Hee Xin Wei (Copyrighted)

Photosynthesis Word equation Chemical equation Simplified chemical equation CarbonDioxide+WaterChlorophyll LightEnergy Glucose+Oxygen+Water 6CO2+12H2OChlorophyll LightEnergy C6H12O6+6O2+6H2O 6CO2+6H2OChlorophyll LightEnergy C6H12O6+6O2 Equation Chlorophyll •Pigment in chloroplast •traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent uses Intake of Carbon Dioxide •In daylight when photosynthesis occurs, the carbon dioxide in the leaf is rapidly used up. •The carbon dioxide concentration in the leaf becomes lower than that in the atmospheric air, so carbon dioxide diffuses from the surrounding air through the stomatal openings into the intercellular air spaces •The surfaces of the mesophyll cells are covered by a thin film of moisture so that carbon dioxide can dissolve in it and diffuses into the cells. Intake of water •The xylem transports water and dissolved mineral salts from roots to the leaves. •Water moves out of xylem vessels and enters cells via osmosis © Hee Xin Wei (Copyrighted)

Limiting Factors •Limiting factors are factors that directly aff ect the process. By increasing the amount of factors, it increases the rate of process •Light intensity, carbon dioxide concentration and temperature are limiting factors on the rate of photosynthesis •Rate of photosynthesis can be measured by 1) Measuring the uptake of CO2 2) Measuring the production of O2 (an example is shown) 3) Measuring the production of carbohydrates 4) Measuring the increase in dry mass Effect of light intensity © Hee Xin Wei (Copyrighted)

Limiting Factors •At a constant temperature and carbon dioxide concentration, the rate of photosynthesis increases with increasing light intensity until it reaches a plateau. •When the plateau is reached, light is no longer the limiting factor in the reaction but other factors such as temperature and concentration of carbon dioxide. This is also called the light saturation point •Raising these factors can increase the plateau •light compensation point is when rate of respiration = rate of photosynthesis, so while rate of photosynthesis is increasing, the net CO2 uptake or O2 release is zero Effect of light intensity © Hee Xin Wei (Copyrighted)