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