Transcript SBI 3U plants 2

Plants: Leaves
Leaves
• Play role in photosynthesis, gas exchange, storage, and
protection from predators.
• Leaf cells absorb energy from sunlight in a chloroplast which
contains photopigments.
• Photopigments are chemicals that absorb particular
wavelengths of red and blue light and reflect green light.
Leaf Structure
• Make sugar and supplies all living organisms with
food and oxygen
• Designed so they can capture the most amount of
sunlight.
• Covered with a waxy cuticle that is produced by the
epidermis. Both provide protection.
• Stomata are little passages on the underside of leaves
that allow for gas and water vapour exchange. Woody
plants have no stomata on the upperside, herbaceous
plants do have stomata on the upperside.
• Stomata are open during the day and closed at night
• Carbon dioxide is used by chloroplasts to perform
photosynthesis
• Carbon dioxide is brought into the plant through the
stoma, while oxygen and water are released into the
atmosphere.
• Photosynthesis cannot happen at night, so the
stomata are closed.
• Each stoma is surrounded by two guard cells that
are kidney-shaped, specialized epidermal cells with
chloroplasts
• Water moves into the guard cells during the day
because of all the ions that move into the cells.
• The inside is thicker, so the outside can expand
more, creating a hole between the two cells.
• Cells within the leaf are the mesophyll cells that have a lot
of chloroplasts and have two layers:
• Palisade layer that are densely packed and have more
chloroplasts
• Spongy layer that are loosely spaced so air can come
in contact with the cells.
• Water loss from the leaves through evaporation is called
transpiration
• The xylem and phloem continue from the stems into the
leaves in special vascular bundles called veins.
• Monocot veins run parallel to each other
• Dicot veins run in a branching network
Leaf Specializations
• Dry climate: thicker cuticle, stomata on
underside.
• Cactus leaves are modified into spines
• Aquatic plants have stomata on the
upperside for gas exchange.
• Onion bulb: stores water and carbs
Leaf Uses
• Provide important nutrients and food energy in
the diets of humans.
• Use them for herbs and spices
• Teas
• They are nutritious (calcium, potassium, iron,
magnesium, vitamins B, C, E, K)
• Use waxy cuticle for polishes, cosmetics,
candies.
Leaves and Chemicals
• Leaves produce chemicals that humans have
used in the past and present as medicinal.
• Research one medicinal plant and report on what
it is used for as homework tonight