2101 - Leaves Flashcards
Main Functions of a Leaf
Provide a site for Photosynthesis.
Regulate Transpiration.
Allow Gaseous Exchange.
Arrise from Nodes on the stem as it grows. Do not arrive from anywhere else.
Physiological Functions
Convert Light, CO2 and H2O into sugars via Photosynthesis.
Regulate Transpiration, thus the uptake of water and nutrients by the plant.
Control the absorption and release of CO2 and O2 via Gaseous Exchange.
Leaf parts
Axially bud (on stem) Petiole (stalk) Leaf Base Lamina (leaf blade) Margin (the edge) Midrib (main vein) Lateral Veins Sub Lateral Veins
Leaf Characterisation
Shape Size Colour Margin Venation Division of the Leaf Blade Arrangement on the Stem
Internal Structure of a Leaf
Cuticle Upper Epidermis Pallisade Mesophyl Spongy Mesophyl Lower Epidermis Stomata Sub-Stomatal Air Chamber Guard Cells
Internal Structure of a Leaf - Epidermis
Single layer of cells, do not contain chlorophyll, but produce Waxy layer cuticle.
Lower epidermis contains the stomata.
Relatively transparent.
Internal Structure of a Leaf - Cuticle
Waxy layer protects against pests, disease and water loss.
Can be thick or thin depending on the plant.
Internal Structure of a Leaf - Palisade Mesophyll
Tightly packed oblong/vertically arranged cells just under the upper epidermis.
Large number of Chloroplasts for optimum Photostynthesis.
Internal Structure of a Leaf - Spongy Mesophyll
Parenchyma cells below the Palisade cells.
Typically less Chloroplasts than Palisade cells.
Loosely packed to facilitate the diffusion of Oxygen, Carbon Dioxide and water vapour.
Internal Structure of a Leaf - Stomata
Breathing pores predominantly in the lower epidermis in Dicots. Allow for Gaseous exchange.
Controlled by Guard Cells in response to light levels and water content of the plant.
Under Active and Passive control.
Ions can be pumped into and out of the guard cells causing them to lose or gain water (osmosis) and open or close.
Water loss by dehydration (loss of Turgor) can also close the stomata. Inhibiting gaseous exchange therefore further water loss via Transpiration.
Leaf Arrangement on Stem - Opposite, Alternate, Whorled.
Opposite - Each node has a pair of leaves.
Cornus spp.
Alternate - Each node has a single leaf, the adjacent nodes point in different directions.
Salix spp.
Whorled - Node has three or more leaves.
Galium spp.
Leaf Arrangement - Simple vs Compound
Simple - Single undivided blade or Lamina. Cannot be sub-divided into leaflets.
May be formed of lobes (Quercus) but gaps do not reach the Mid Rib.
Compound - Blade is divided into several leaflets. Identified by the lack of Axially bud. (Midrib may be called Rachis)
Simple, Lobed, Palmately Compound, Pinnately Compound
Simple - Fagus syllabic
Lobed - Quercus roubar
Palmate - Aesculus hippocastanum
Pinnate - Fraxinus excelsior
Leaf Adaptions
Tendril Spines Water Storage Carnivorous Perennation
Leaf Adaptions - Tendril
Climbing by Tendril, modified leaflet.
Support and height to increase availability of Light, Air and chance of Pollination.
Pisum sativum (Garden Pea)
