Leaves
have many functions
1. Leaves are the photosynthetic organ of
a plant; usually they are composed of 2
parts: the blade and petiole.
2. Leaves are the main site of evaporation
of water from the plant.
3. Gas exchange carbon dioxide for
photosynthesis and oxygen from
photosynthesis and for respiration are
usually exchanged through the leaves.
Parts of a Typical Leaf
Function of Leaf Tissues
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Cuticle – waxy covering prevents water loss
Upper and Lower Epidermis - Protection
Palisade Mesophyll Cells – main photosynthetic tissue
Bundle Sheath Cells - give some rigidity and
protection to the enclosed vascular tissue.
Xylem – transports water
Phloem – transports sugars
Spongy Mesophyll Cells – create spaces for gas
exchange
Guard Cells – regulate the flow of water
Stomata – openings in the leaf, exchange of gases
Vein (Vascular bundle)– transportation
Sclerenchyma – strength and support
Most of the photosynthesis takes
place in the palisade cells… in the chloroplasts.
Stomata
-are the "pores" in leaves
(and stems) through which
CO2 is taken in and O2 is
released during
photosynthesis.
Plants control when stomata
are open or closed and the
width of the opening
(formed by two guard cells
that expand and contract to
open and close the space
between them).
Leaf Types
Leaf Margins
Leaf Arrangements
Flowers
are the reproductive structures of the plant.
- Attract pollinators, and protects the reproductive
structures
- Protects young flower
Site where the eggs are produced base of the flower
-
The Male Reproductive Structures
are called the Stamens.
They consist of two
parts:
• The anther -- a small
case in which the
pollen grains form
• The filament -- a
slender stem that
supports the anther
The Female Reproductive
Structure is called the Pistil.
It consists of three parts:
• The stigma -- the pollen
grains stick to this small
sticky pad
• The style -- the pollen
grains grow down through
this stem-like cylinder
• The ovary -- this is where
the young seeds (eggs)
wait for the chromosomes
in the pollen (sperm), and
where they grow into
mature seeds…. Which
contain the embryos.
also called a Carpel
Pollination
is the transfer of pollen from the male part of the
plant to the female part of the plant.
Insect Pollination
The pollen is transferred to
the stigma by an insect.
Water Pollination
orchids are usually water-pollinated plants.
The pollen is
transferred
(washed) to the
stigma by water
(rain).
Wind Pollination
conifers are usually wind-pollinated plants.
The pollen is transferred (blown) to the stigma by wind.
Self-Pollination
Pollen from plant A
pollinates plant A…
the offspring now is
composed of the
DNA from only one
parent.
Self-pollination
ensures genetic
continuity….. every
generation is
genetically identical.
Cross-Pollination
Pollen from plant
B is transferred
to plant A… the
offspring now is
composed of the
DNA of both
parents. Crosspollination
creates diversity.
Germination
a plant starts to grow…. Germination is
triggered by Cytokinin.
Gymnosperms (cone-bearing plants)
Gymnosperms
reproduce using
cones
• The Female cone is
called the “Seed”
cone… it contains the
eggs (which become
seeds after
fertilization)
• The Male cone is
called the “Pollen”
cone… the pollen
Double Fertilization
each pollen grain contains two sperm cells….. One sperm cell fertilizes
the egg (2n - which becomes the embryo), the other fertilizes the polar
nuclei. (3n – which eventually becomes the endosperm)
Seeds
- Store and digest foods
Hypocotyl - Embryonic Stem
Embryonic leaves - Epicotyl
Embryonic root -
- Opening for sperm tube
- Attachment point to Ovule
- Protection
Monocot and Dicot Seeds
Monocots have one cotyledon (seed leaf), Dicots have two cotyledons (seed leaves)
Fruit
a mature plant ovary that encloses a seed, or seeds, and provides
nourishment and protection
Pericarp
Floral Tube
Endocarp
Mesocarp
Exocarp
Seed
Fruit
a mature plant ovary that encloses a seed, or seeds, and provides
nourishment and protection