The purpose of reproduction is to produce offspring.
Sexual reproduction
A plant produced by sexual reproduction is genetically different to the parent plant. Sexual reproduction begins with the production of flowers from the adult plant. Pollen (male gametes) forms by meiosis in the anther of the flower. Ovules (female gametes) form in the ovary.
Pollination
Transfer of pollen from the anther to the stigma is called pollination. Pollination is successful only if the pollen is transferred between plants of the same species. Transfer of pollen from an anther in a flower of one plant to the stigma of a flower on another plant of the sames species is called cross-pollination. Self-pollination occurs when the transfer is within the same plant. Some flowers eg sweet pea are shaped to always result in self-pollination
Insect pollination occurs when an insect transfers the pollen. Plants that have insect pollination have brightly coloured flowers containing scent and nectar to attack insects. They produce small amounts of pollen with a rough surface to stick to the insect body.
Wind pollination occurs when pollen is blown from anther to stigma. Wind pollinated plants produce large amounts of light, smooth, round-shaped pollen, suitable for wind transport.
Wind pollinated flowers are often green or white because there is no need to attract pollinators. The flowers have large anthers that hang outside the flower so pollen is released easily into the wind. The stigma is feathery and hangs outside to catch pollen
Fertilisation
if pollen from a species of plant lands on a stigma of a plant from the same species, chemicals on the stigma causes the pollen to grow. The pollen grows a thin tube down the style into the ovary where the genetic material in the pollen joins with the genetic material of an ovule. This joining is fertilisation - a plant embryo forms as a result of fertilisation.
Seeds
After fertilisation, the ovules in the ovary develop into seeds. Each seed is covered by a protective testa. The seeds contains the embyro plant - radicle (first root) or plumule (first shoot), and food stored in the cotyledons. The micropyle is a small hole in the testa that allows water to enter seed to begin germination.
Fruits and dispersal
after fertilisation, the ovary of the flower develops into a fruit. Some fruits are dry and hard eg kowhai and some are soft and fleshy eg tomato. The fruit protects the seeds while they are being transported away from the parent plant - this is dispersal of the seeds. Dispersal reduces competition between parent and offspring and among offspring for resources like light and nutrients.
Different plants have different methods of seed dispersal
Explosive - hard dry fruit, forms a pod. In warm conditions the pod splits and twists spreading light round seeds eg gorse
Float - A light waterproof fruit forms carried by water eg coconut
Hooks - Fruit has a hook which catches animal fur or feather bidibids
Succulent - Fleshy fruit eaten by animal, transported away in gut
Wind - light fruit with a special shape to allow travel on the wind eg dandelion
Asexual reproduction (vegetative reproduction)
Production of new plants without making of seeds. new plants have the same genetic make-up as the parent. Asexual reproduction is quick and does not require a plant to use energy to make flowers, pollen, and fruits. Large number of offspring that grow close to the parent plant are produced. These plants can produce sexually at a different time of year.
Range of methods of asexual reproduction
Runner and stolon- shoots that grow above ground surface eg strawberry
Tuber - Swollen underground root with small buds under skin eg potato, kumara
Bulb - swollen underground leaf scale eg daffodil
Corm - swollen underground stem eg gladioli
Rhizomes - Thick underground stems that grow sideways eg iris
In some species of plants, new plants can grow from part of a plant - new dandelion plants can grow from a broken part of the main root.
Photosynthesis
photosynthesis is the process by which plants make glucose from carbon dioxide and water. To do this, green plants need chlorophyll (green pigment) and energy from light. Glucose is stored as starch when it is produced.
carbon dioxide + water ----------chlorophyll, light ----- glucose + oxygen
Leaf structures
Leaves are the main plant structure involved in photosynthesis. Leaves have the following adaptations to help them with photosynthesis.
Thin - gases don't travel far
Flat - a large surface area to trap light
Arranged on plant to trap most possible light
Green due to chlorophyll
Covered in waxy cuticle to stop leaf drying out.
The internal structure of leaves also has adaptations for carrying out photosynthesis
diagram
Testing leaves for the presence of starch
The presence of starch in a leaf is used to indicate photosynthesis has been occuring. Glucose made from photosynthesis is stored as starch in the right conditions. Iodine can be used to test for starch it turns brown to blue-black when starch is present.
Before a plant or leaf is used to test a factor for photosynthesis, it is destarched by putting it in the dark for two or three days so the plant uses up any stored starch.
To test for starch
1- boil the leaf to remove waxy cuticle
2- boil leaf in meths to remove chlorophyll as green colour would hide colour change with iodine
3- wash leaf to remove meths
4- add 3 to 4 drops of iodine
5- a blue-black result indicates starch
Factors affecting photosynthesis
-increasing the amount of carbon dioxide increases photosynthesis rate until some other factor becomes limiting eg chlorophyll amount
-increasing light intensity increases rate , up to a point
-increasing temperature increases rate, up to the optimum after which increasing temperature decreases rate of photosynthesis as enzymes are denatured
-If there is little magnesium in the soil, plant makes reduced chlorophyll
-When there is less water, the stomata closes. this limits the CO2
-changing wavelenght (colour) of light changes rate. chlorophyll does not absorb green light (reflected). Blue and red light produces highest rate of photosynthesis, yellow produces lower and green the lowest.
To show light is necessary for photosynthesis
diagram
to show co2 needed for photosynthesis
diagram
to show chlorophyll needed for photosynthesis
diagram
oxygen needed for photosynthesis
diagram