World of Plants
Standard Grade Biology
The Importance of Plants
• Green plants make food for themselves
and for animals by photosynthesis
• They use up carbon dioxide and release
water and oxygen
• They provide habitats for animals
• We get raw materials, food and
medicine from plants
• They improve our surroundings
Uses of Plants
Food
Raw Materials
Medicines
Wheat for bread
Jute for string
Foxglove for digitalis
Palms for oil
Flax fibres for linen
Poppies for morphine
Sugar cane
Flowers for perfume
Cinchona tree for
quinine
Grapes for wine
Wood for timber
Timber production
Site Preparation
Planting
Thinning
Felling and Removal
Effects of Reducing Plant Species
• Human activities are having an adverse
effect on plants in the environment e.g.
destruction of the rainforests
• Animals are losing habitats
• The number of species is being reduced
and so is the biodiversity
Potential Uses of Plants
• Many species of plants could have uses
not yet discovered e.g. as medicines,
food etc
• If destruction of the rainforests
continues, these uses may be lost
before they are even discovered
Flower Structure
Pollination
• Cross pollination is
the transfer of
pollen from anther
to stigma of another
flower
• Self pollination is
the transfer of
pollen from anther
to stigma of the
same flower
Different types of pollen grains
Wind and Insect Pollination
Insect Pollination
Wind Pollination
Pollen Tubes
• Pollen lands on the stigma
• The pollen grain containing the male
nucleus starts to grow a pollen tube.
• The male nucleus travels down this tube
to the ovules in the ovary
Pollen tube
Male
nucleus
Pollen
grain
stigma
ovary
Male nucleus travels
down pollen tube to
the female nucleus
inside the ovule.
Ovule
containing
female
nucleus
Fertilisation
• The male nucleus travels down the tip of
this pollen tube to the ovules in the
ovary
• The male nucleus and female nucleus
fuse
• This is called fertilisation.
The Seed
• The fertilised egg now grows into a
seed- containing:– An embryo plant
– Food store (starch)
– Seed coat
• The ovary now becomes a fruit.
• This fruit can be hard + dry or soft +
fleshy
Seed dispersal
•
Seeds need to be
dispersed to
reduce
competition. Plants
compete for
1.
2.
3.
4.
minerals
water
space
light
Seed Dispersal
• Seed dispersal helps to scatter seeds to
distant places away from the parent.
• 3 methods
– By wind
– By animal internal-eaten
– By animal external – stick to animal fur
The seeds are
attached to
parachutes
which help to
catch the wind.
Wind
The wings catch
the wind
Animal -external
The hooks help the
seed to stick to
animal fur
Animal -internal
The bright red colour
of the berries attract
insects + birds. The
fruit is juicy and the
seed is ingested. It
eventually ends up in
animal droppings and
far away from the
parent plant.
Seed Structure
Functions of the Parts of a Seed
Part
Function
Seed Coat
Tough covering protects the seed
from damage by soil insects, soil fungi
and the gut enzymes if eaten
Embryo Plant
Embryo root and shoot will become
the new plant after germination
Food Store
Provides energy for growth until the
plant is able to photosynthesise for
itself
Seed Germination
• Once the seed has been scattered it will land
and start to germinate.
• It needs
– Water – to allow enzymes to digest food store and
soften the seed coat.
– Oxygen –for respiration to release energy from
the food store (seeds do not photosynthesise)
– Warmth – for optimum temperature for
enzymes to work, between 15 and 30ºC in plants
Asexual Reproduction
Tubers
• Are underground food stores
• Are swollen stems
• E.g. potato, dahlia
Asexual Reproduction
Runners
•
•
•
•
Are side shoots growing from the parent
Grow long and bend until they touch the ground
Grows roots where it touches the ground
E.g. spider plant, strawberry
Asexual Reproduction
Bulbs
• Are thick fleshy
leaves full of stored
food
• E.g. onions, daffodils
Artificial propagation - Cuttings
• Plant stem is cut and grown in water/moist
compost to develop roots.
• Hormone powder accelerates root formation
Asexual Reproduction - Grafting
Grafting
Fruit Salad trees can have
as many as 7 different
fruits of the same family
grafted onto one tree.
You can get:citrus trees.
multi-apple trees
multi-pear trees
stone fruit-peaches,
plums, apricots,
nectarines
Advantages of Artificial
Propagation
• Quick way to produce a large number of
plants
• Plants will be identical to the parent
• Rare plants can be saved from
extinction
Sexual Vs Asexual Reproduction
Asexual Reproduction
(natural)
Sexual Reproduction
Only 1 parent required
2 parents , more variation, more
able to adapt to changes
Young plants get food and water
from parent, can grow more
quickly but can get overcrowded
Seeds are tough and can stay
dormant until conditions are
favourable
Young plants less vulnerable than
seedlings
Seeds more likely to be dispersed
away from parent , less
competition
Young plants identical to parent –
good features passed on
- bad features also passed on
More variation arises due to
chance, some plants will have
better characteristics than
either or both parents
Warning!
• Do not confuse artificial propagation
with asexual reproduction
• Asexual reproduction is a natural
process
• Artificial propagation is how man
manipulates plants to produce the types
of plant he requires
How Plants Make Food
How Plants Use the Glucose they Make
• Store it as starch
• Use it immediately in respiration
• Use it as structural material (cellulose)
Transport in Plants
• Plants take in water and dissolved minerals
through the roots
• Root hairs provide a large surface area for
absorption
• Water moves from cell to cell until it reaches
the xylem vessels
• Xylem carries water and dissolved minerals to
the leaves for photosynthesis
• The sugars made in photosynthesis are
carried from the leaves in phloem tubes
Xylem
• Xylem vessels transport
water + minerals.
• From roots upwards to
leaves.
• Xylem vessels are dead.
• They have rings of lignin
to support the plant.
• Note that the lignin
strengthens the cell
wall but supports the
plant
Phloem
• Transports food
(sugars) from leaves
downwards to rest of
plant.
• Unlike xylem phloem is
living tissue.
• Phloem tubes have
sieve plates to allow
food through
• And companion cells to
control the sieve tube
Vascular Bundles
• Xylem and phloem are sometimes found
together as vascular bundles
Structure of a Leaf
Waxy cuticle
chloroplast
Upper epidermis
Palisade mesophyll
xylem
phloem
Spongy mesophyll
Lower mesophyll
Guard cell
stoma
Air space
Structure
Function
Upper and lower
epidermis
Transparent cells with few or no chloroplasts
so that light can pass through
Palisade mesophyll
cells
Main site of photosynthesis, regular shape
and tightly packed, have a lot of chloroplasts
and get the most light
Spongy mesophyll
cells
Irregular shapes with air spaces to allow
diffusion of gases
Xylem
Transports water and dissolved minerals to
leaf
Phloem
Transports the sugars made by
photosynthesis to all part of the plant
Guard cells
Change shape to control the opening and
closing of the stomata which allow gases in
and out of the leaf
Guard Cells and Stomata
• Guard cells control the
opening and closing of
the stomata
• At night the guard cells
become flaccid and less
curved, closing the
stoma
• In daylight they become
turgid and curve,
opening the stoma
• Most of the stomata are
found on the lower
surface of the leaf