Post on 23-Feb-2016
description
12.2 Leaves
Pages 546-551
Tea leaves
• Camellia sinsensis
Leaves
Site of :• Photosynthesis• Gas exchange• Storage• Protection from predators
Photosynthesis
• Glucose is used for fuelling cellular processes and as a building block for structural materials (cellulose)
• Oxygen is produced, required by all organisms for cellular respiration
• Carbon dioxide is a greenhouse gas, so photosynthesis reduces Carbon dioxide in the atmosphere
chloroplasts
• Organelles in plants, site of photosynthesis
Photopigments
• Pigments absorb certain wavelengths of light and reflect others
• Chlorophyll absorbs red and blue light and reflects green light
Accessory pigments
• Accessory pigments include carotenoids, flavonoids and betalains
• Absorb different colours of light
Protection
• Shape. For example: sharp spines in cacti• Surface hairs.• Toxins or bad-tasting chemicals to deter
herbivores
Structure of Leaves
• Blade…flat part of the leaf• Petiole…stalk-like structure attaches leaf to
stem• Simple leaf or compound
leaf
Veins
• Venation is the pattern of veins• Parallel veins are seen in monocots• Branching veins are seen in eudicots
Internal Leaf Structure
Layers
• Waxy cuticle - prevents water loss-acts as a barrier for bacteria, mould and insects
Epidermis
• Transparent cells• Single layer of cells• No photosynthesis
Mesophyll
• Chloroplasts are found in mesophyll cells• Palisade…elongated, tightly packed, contain
many chloroplasts• Spongy…loosely packed, large air spaces
Stoma (or stomata)
• Tiny pores through which gases move• Guard cells control the opening and closing of
the stomata
Specialized Leaves
• Storage of water and carbohydrates.example: onions
Storing water
for example: aloe vera
Protection
• Cacti Tobacco
Protection against freezing
• Conifers have needle-shaped leaves that shed easily, have thick waxy cuticles, sunken stomata, and may contain antifreeze chemicals.
Human uses for leaves
• Teas• Herbs and spices• Food wraps (cabbage, grape, banana or
bamboo leaves)
Dark leafy greens
• Contain Calcium, magnesium, potassium and iron
• Vitamins B, C, E, and K• Beta-carotene, lutein and zeozanthin, omega-
3 fats
Other uses for leaves
• Waxes• Religious ceremonies• Construction materials
Drugs
• Digitalis is used to treat heart disease
Vincristine and vinblastine
• Treats childhood leukemia and Hodgkin’s disease.
Psychotropic Drugs
• Alter perception, emotion or behaviour• THC tetrahydrocannabinol• Coca …cocaine