B6 Organisation in Plants Flashcards
plants organs
roots, stems,
leaves (contain many tissues that work together to perform photosynthesis)
waxy cuticle
makes leaf waterproof
upper epidermis
• single layer of cells
• protects against water loss
• transparent - allows light to pass through
palisade mesophyll
• tightly packed cells
• lots of chloroplasts (absorb light for photosynthesis)
spongy mesophyll
• spherical cells
• lots of air spaces to allow gases to diffuse quickly
• large SA:V ratio - increase gas exchange
guard cells
control opening and closing of the stormata
when plants has lots of water, they become turgid (swell up) and curve away from each other (cell wall on inner surface is very thick), this opens stomata
stomata (definition)
tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf
stomata (details)
on the underside - placement reduces water loss through evaporation (as it is exposed to less sunlight/heat)
control gas exchange and water loss from leaves by:
- allowing diffusion of carbon dioxide into the plant (for photosynthesis)
- allowing diffusion of oxygen out of the plant
opened and closed by guard cells
transpiration
constant movement of water up the plant
water lost through the stomata by evaporation - water pulled up through roots and through xylem.
importance of transpiration
provides water to cells to keep them turgid
provides water to cells for photosynthesis
transports mineral ions to leaves
xylem vessel
translocation
movement of dissolved sugars from leaves to rest of the plant through the phloem
importance of translocation
moves dissolved sugars made in the leaves during photosynthesis to other parts of the plant
- allows respiration, growth, glucose storage
phloem vessel
4 factors affecting transpiration (what, how and why)
how plants control water loss
waxy, waterproof cuticle on the leaves - thick and shiny in hot environments
stomata are on underside
wilting: leaves collapse and hang down - reduces surface area
stomata can close (although this stops photosynthesis)
root hair cells
increase absorption of water and mineral ions into the root by increasing surface area
contain lots of mitochondria to transfer energy (used to take in minerals by active transport)
exam q: why is rate of water uptake different to rate of transpiration (2)
rate of transpiration < rate of water uptake
some water taken in is used in photosynthesis
vascular bundle
structure in stems where xylem and phloem are
exam q: describe how a student could take samples from a leaf to count the number of stomata present (3)
place several strips of (nail) varnish on the leaf / several
leaves and allow to dry
peel the varnish off the leaf and place on a microscope
slide
observe the strip of varnish (under a set magnification)
and count stomata in the field of view
exam q: how are the tissue inside a leaf adapted to perform photosynthesis (6)
top of leaf:
(tightly packed) palisade cells
contain many chloroplasts for photosynthesis
upper cells protected by epidermis
waxy surface reduces water loss from upper surface
middle of leaf:
spongy mesophyll cells
have large air spaces / surface area to maximise gas
exchange
xylem supplies water for photosynthesis
phloem transports dissolved sugars from
photosynthesis to plant
lower part of leaf:
stomata open or close through action of guard cells
to let carbon dioxide diffuse in
to allow oxygen / water vapour to diffuse out
