Download plant tissues - WordPress.com

4.4 PLANT
TISSUES
Working Together
LEAVES
• Leaves are highly specialized structures with one primary
function
Photosynthesis:
chlorophyll
light energy + carbon dioxide + water

glucose + oxygen
• glucose produced can be converted into carbohydrates used
as building blocks for plant’s structures and functions
Absorbing Light
• Thin, wide leaves with large surface area absorb
sunlight best
• In the chloroplasts, Chlorophyll absorbs the light
• Chloroplasts are found in the
palisade layer and the spongy
mesophyll of a leaf
• These are part of the
ground tissue system
• The tightly packed palisade
layer capture the maximum
amount of light while the
loosely packed
spongy mesophyll
allow gases to move
around (CO2 & O2)
Obtaining Carbon Dioxide
• the epidermis of the leaf has cells that produce a thin layer of
wax called the cuticle
• The cuticle prevents water loss and the diffusion of gases from
the surface of the leaf
• Gases enter and leave through openings called the stomata
which are found on the underside of the leaf
• They are surrounded by special epidermal cells called the
guard cells
Controlling Stomata
• Guard cells around the stoma alter
their shape to open and close
• Stomata open to let CO2 enter.
• Stoma respond to the water level
in the leaf
• Good water supply they expand and bend apart—open
• Water shortage, they become soft and collapse—closed
• Stomata close on sunny or windy days to prevent from drying
out
• Guard cells also respond to light levels and close at night when
photosynthesis is not possible
Obtaining Water
• root hairs: Long thin epidermal cells on
the roots absorb water from the
soil by osmosis
• Root hairs increase
the surface area for water
absorption
• Water is then transported up the
from the roots through xylem
to the stem and leaves
Comparing Plant & Animal Systems
• Similarities
• Vascular bundles are similar to veins and arteries
• Differences
• Animals actively use a heart to pump blood around organism
• Plants passively acquire water and distribute it