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)
Photosynthesis
• Oxygen is produced, required by all organisms
for cellular respiration
Photosynthesis
• 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 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 Ca, Mg, K and Fe
• Vitamins B, C, E, and K
• Beta-carotene, omega-3 fats etc.
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