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Reproduction - Coggle Diagram
Reproduction
Sexual Reproduction in Plants
In flowering plants, male and female reproductive structures can be found in the same individual plant. The organ of sexual reproduction is the flower.
Male gametes are found in pollen grains and produced in the anthers of the flower.
Female gametes are found in ovules and produced in the ovary of the flower.
Parts of a typical Flower
Petals
Petals are usually brightly coloured and sometimes scented.
They are arranged in a circle or a cylinder.
Sometimes they are joined together to form a tube and the individual petals can no longer be distinguished.
The colour and scent of the petals attract insects to the flower; the insects may bring about pollination.
The flowers of grasses and many trees do not have petals but small, leaf-like structures that enclose the reproductive organs
Carpel
Carpel is the ovule-bearing female reproductive organ of flowering plants
Sepals
Outside the petals is a ring of sepals. They are often green and much smaller than the petals. They may protect the flower when it is in the bud.
Stamens
The male parts of the flower consisting of the anther held up on the filament
Anthers
Produce male gametes (in pollen grains)
Stigma
The top of the female part of the flower which collects pollen grains
Ovary
The bottom of the female part of the flower, produces the female gametes (in ovules)
Nectary
May be present to produce sugary nectar to attract insects
Pollen
Pollen grains contain the male gametes (sex cells) required for fertilisation
Pollination
The transfer of pollen from the anthers to the stigma is called pollination.
The anthers split open, exposing the microscopic pollen grains
The pollen grains are then carried away on the bodies of insects, or simply blown by the wind, and may land on the stigma of another flower
Types of pollination
Wind Pollination
Insect Pollinating
Fertilization
Pollination is complete when pollen from an anther has landed on a stigma.
If the flower is to produce seeds, pollination has to be followed by a process called fertilisation.
In all living organisms, fertilisation happens when a male sex cell and a female sex cell meet and join together (they are said to fuse together). The cell that is formed by this fusion is called a zygote and develops into an embryo of an animal or a plant
For fertilisation to occur, the nucleus of the male cell from the pollen grain has to reach the female nucleus of the egg cell in the ovule, and fuse with it.
The importance of water, oxygen and temperature in germination
Use of water in the seedling
Most seeds, when first dispersed, contain very little water.
In this dehydrated state, their metabolism is very slow and their food reserves are not used up.
The dry seeds can also resist extremes of temperature and desiccation.
Water is absorbed firstly through the micropyle, in some species, and then through the testa as a whole.
Once the radicle has emerged, it will absorb water from the soil, particularly through the root hairs.
The water that reaches the embryo and cotyledons is used to:
activate the enzymes in the seed
● help the conversion of stored starch to sugar, and proteins to amino acids
● transport the sugar in solution from the cotyledons to the growing regions
● expand the vacuoles of new cells, causing the root and shoot to grow and the leaves to expand
● maintain the turgor of the cells and thus keep the shoot upright and the leaves expanded
● provide the water needed for photosynthesis once the plumule and young leaves are above ground
● transport salts from the soil to the shoot
Uses of oxygen
In some seeds the testa is not very permeable to oxygen, and the early stages of germination are probably anaerobic.
The testa when soaked or split open allows oxygen to enter.
The oxygen is used in aerobic respiration, which provides the energy for the many chemical changes involved in mobilising the food reserves and making the new cytoplasm and cell walls of the growing seedling.
Reproduction is the process of making more of the same kind of organism
There are two types of reproduction that you need to be aware of: Asexual reproduction. Sexual reproduction.
Sexual reproduction
Sexual reproduction involves the joining of two sex cells, or gametes during fertilisation. Organisms produced by sexual reproduction have two parents and are genetically similar to both but not identical to either.
Sexual reproduction involves the production of sex cells. These sex cells are called gametes and they are made in reproductive organs.
The process of cell division that produces the gametes is called meiosis join together to form a single cell called a zygote.
The zygote then grows into a new individual
In flowering plants the male gametes are found in pollen grains and the female gametes, called egg cells, are present in ovules.
In animals, male gametes are sperm and female gametes are eggs.
In both plants and animals, the male gamete is microscopic and mobile (i.e. can move from one place to another).
The sperm swim to the ovum; the pollen cell moves down the pollen tube
The female gametes are always larger than the male
Advantages of sexual reproduction
In plants, the gametes may come from the same plant or from different plants of the same species.
In either case, the production and subsequent fusion of gametes produce a good deal of variation among the offspring
This may result from new combinations of characteristics, e.g. petal colour of one parent combined with fruit size of the other. It may also be the result of spontaneous changes in the gametes when they are produced.
Disadvantages of Sexual Reproduction
some combinations will produce less successful individuals.
On the other hand, there are likely to be some more successful combinations that have greater survival value or produce individuals which can thrive in new or changing environments.
In a population of plants that have been produced sexually, there is a chance that at least some of the offspring will have resistance to disease. These plants will survive and produce further offspring with disease resistance.
The seeds produced as a result of sexual reproduction will be scattered over a relatively wide range. Some will land in unsuitable environments, perhaps lacking light or water. These seeds will fail to germinate. Nevertheless, most methods of seed dispersal result in some of the seeds establishing populations in new habitats.
The seeds produced by sexual reproduction all contain some stored food but it is quickly used up during germination, which produces only a miniature plant. It takes a long time for a seedling to become established and eventually produce seeds of its own.
Sexual reproduction is exploited in agriculture and horticulture to produce new varieties of animals and plants by cross-breeding.
asexual Reproduction
Asexual reproduction only involves one parent so there is no joining of sex cells during fertilisation. Organisms produced by asexual reproduction are genetically identical to each other and their parent. They are clones.
Advantages
No gametes are involved and all the new plants are produced by cell division from only one parent.
they are genetically identical; there is no variation. A population of genetically identical individuals produced from a single parent is called a clone.
This has the advantage of preserving the ‘good’ characteristics of a successful species from generation to generation.
Disadvantages
Overcrowding- fighting for food
Prone to extinction
No variation/biodiversity
Harmful genes transferred
Examples
Asexual reproduction in flowering plants
(vegetative propagation)
When vegetative propagation takes place naturally, it usually results from the growth of a lateral bud on a stem which is close to, or under, the soil.
Instead of just making a branch, the bud produces a complete plant with roots, stem and leaves
When the old stem dies, the new plant is independent of the parent that produced it.
An unusual method of vegetative propagation is shown by Bryophyllum
Learn more:-
Asexual reproduction in animals
Some species of invertebrate animals are able to reproduce asexually.
Hydra is a small animal, 5–10 mm long, which lives in ponds attached to pondweed. It traps small animals with its tentacles, swallows and digests them.
Hydra reproduces sexually by releasing its male and female gametes into the water but it also has an asexual method,
Cross breeding
Crossbreeding is defined as the process or the act of producing offspring particularly through mating two purebred individuals but come from different breeds, varieties, or even species.
Example
For example, suppose one variety of wheat produces a lot of grain but is not resistant to a fungus disease. Another variety is resistant to the disease but has only a poor yield of grain. If these two varieties are cross-pollinated offspring should be disease-resistant and give a good yield of grain (assuming that the useful characteristics are controlled by dominant genes).
A long-term disadvantage of selective breeding is the loss of variability.
By eliminating all the offspring who do not bear the desired characteristics, many genes are lost from the population.
At some future date, when new combinations of genes are sought, some of the potentially useful ones may no longer be available
Sexual Reproduction in Humans
Menstrual Cycle
During the process, the lining of the uterus is prepared for pregnancy. If implantation of the fertilised egg into the uterus lining does not happen, the lining is then shed. This is known as menstruation.
The menstrual cycle is a recurring process which takes around 28 days.
Several hormones are involved in the menstrual cycle of a woman:
follicle stimulating hormone (FSH) causes the maturation of an egg in the ovary
Produced by the Pituitary gland
luteinising hormone (LH) stimulates the release of the egg
Produced by the Pituitary gland
oestrogen is involved in repairing and thickening the uterus lining, while progesterone maintains it
Produced by the ovaries
Progesterone
Maintains the lining of the uterus during the middle part of the menstrual cycle and during pregnancy
Produced by the ovaries
If a woman becomes pregnant, the placenta produces progesterone. This maintains the lining of the uterus during pregnancy and means that menstruation does not happen.
Relationship between hormones during Menstruation
Days 1 to 12 - oestrogen gradually increases and peaks approximately on the 12th day. Progesterone, LH and FSH stay approximately at the same levels and begin to increase slightly from around day 12.
FSH and LH patterns are very similar and peak during ovulation at approximately 14 days during this cycle. They drop sharply on day 15 and stay constant until day 28.
Oestrogen drops during days 13 and 14, and progesterone continues to gradually increase until about day 21, when it slowly beings to decrease again. Oestrogen mirrors this shape and also has a second lower peak at about day 21.