Year 8 Reproduction Notes 2014 (Mr. Hung)
Name: ______
Part A: Reproduction in Humans (Health Education)
Reproduction is the process by which new living things are produced to replace those which die from disease, old age or are eaten by predators. Many animals (including humans) and plants reproduce by sexual reproduction.
Sexual reproduction requires sex cells. Female animals produce eggs from the ovaries, male animals produce sperm from the testes.
Egg cell Sperm cell sperm about to enter the ovum
To make a new individual, a male and female sex cell must fuse (join) together. This is called fertilisation. In humans fertilisation occurs in the oviduct(egg tube).
Part B: Two Main Types of reproduction
There are two types of reproduction: asexual and sexual.
Asexual reproduction
· one parent dividing in two to give new individuals.
· is much quicker than sexual reproduction
· produces individuals which are identical to the parent. This can be a disadvantage as all individuals have the same weaknesses e.g. prone to the same illnesses.
Sexual reproduction
· involves two parents (one male, one female) producing sex cells which join together to make a new individual
· takes much longer than asexual reproduction
· produces individuals which are different from one another
/ Asexual Reproduction / Sexual Reproduction /Number of organisms involved / One parent needed / Two parents are required to mate
Cell division / Simple – mitosis – one to two with same genetic material / Cells divide by Meiosis – one to 4 cells called sex cells or gametes
Types / Budding, binary fission, vegetative reproduction, fragmentation, spore formation
Advantages / Time Efficient; no need to search for mate, requires less energy / Variation, Unique., organism is more protected
Disadvantages / No variation - if the parent has a genetic disease, offspring does too. / Requires two organisms, requires more energy
involvement of sex cells / no formation or fusion of gametes(sex cell) / formation or fusion of gametes(sex cell) occurs - fertilisation
found in / lower organisms – bacteria, sponges / higher invertebrates and all vertebrates
Part C: Different types of Asexual Reproduction
Type / What is it? / ExamplesBinary fission / simplest form of asexual reproduction - parent organism divides into two parts that are equal - daughter cell is identical to parent / Bacteria and protozoans such as Euglena, Amoeba, Paramecium.
Budding / parent cell divides into two unequal parts or a smaller body part is grown to become an adult. / Yeast, sponge and hydra
Spore formation / spores are released by parent organism, spores germinate and grow to form new individuals / Bread mould, mosses and ferns
Vegetative reproduction or Propagation / a type of asexual reproduction found in plants where new independent individuals are formed without the production of seeds or spores. / Onion, Strawberry, Carrot, Potato
Fragmentation
Or Regeneration / a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. / Some flat worms (eg. Planarian), some echinoderms like star fish and sea anemones.
Parthenogenesis / an unfertilized egg develops into a new individual. / water fleas, aphids, stick insects, some ants, bees and parasitic wasps), some reptiles, amphibians and fish
Cloning / the production of multiple, identical offspring. A clone is an animal who is genetically identical to its donor "parent / Lamb, cow, fish
Vegetative propagation involves artificial and natural means by which plants reproduce.
Types of Vegetative Propagation
Types / What is it? / ExamplesBulb / consists of fleshy layers of leaves that store food for the developing plant; there are lateral (side) buds which may grow to form new plants. / Onion, garlic, lily, tulip, Daffodil
Stem Tuber / swollen underground stems that can develop into new plants; a tuber has leathery skin and lots of eyes / potato, and turnips
Corm / contain a solid mass of stem tissue, rather than concentric rings of leaves; this consists of one or more internodes with at least one growing point. / Gladiolus, Taro, Freesia
Runner or Stolon / some plants produce long side shoots that develop roots, eventually forming a new plant / Strawberry, some grasses, spider plant.
Rhizome / these are underground stems that can develop into new plants. They grow sideways in the soil and have a shoot with leaves. / Ginger, Asparagus, Bamboo, Iris, Banana
Root Tuber / Swollen roots are full of stored food / Carrot and beetroot, sweet potato and yam
Sucker / a new stem grows from the base of an old one or root, forming a new plant. / Banana, Rose
Cutting / pieces of roots, stems, or leaves are cut and develop into new plants / African violet
Layering / a portion of an aerial stem grows roots while still attached to the parent plant and then detaches as an independent plant. / purple and black raspberries, trailing blackberries.
Grafting / a cutting from one plant, called the scion, is attached to the main body of a rooted plant, the stock / Grapes, seedless oranges
Tissue Culture / a technique used to grow plants from pieces of plant tissue / African Violet
· Asexual reproduction in plants is called Vegetative Propagation.
· In Vegetative Propagation, the roots, stems, or leaves can grow a new plant.
· 5 kinds of natural vegetative propagation:
1. Bulbs: a short underground stem surrounded by colourless leaves that store food and protect the bulb.
2. Corms: contain a solid mass of stem tissue, rather than concentric rings of leaves; this consists of one or more internodes with at least one growing point.
3. Tubers: a underground stem that stores the food created above ground. A tuber contains “eyes” that will sprout a new plant. These eyes are also called buds.
4. Runners: the main stem of a plant grows straight up through the dirt and new plants grow from it. Each runner has a bud at the end for the new plant.
5. Rhizomes: a thick underground stem that stores food. Rhizomes contain nodes that develop into new plants.
· 3 kinds of artificial vegetative propagation:
1. Cuttings: created by cutting a stem or leave from a plant and place into water. After a few days you will be able place into soil.
2. Grafting: created by attaching a stem cutting of one plant to another plant and they begin to grow together. Can only be done with plants that are related.
3. Layering: when the stem of plant does not hold the plant up, and drooped part touches the earth. When this happens roots start to grow from the leaf/flower touch the earth. Can be either artificial or natural.
Part D: Development in Other Animals
Some young are very different from their parents. Metamorphosis is a complicated process that some animals undergo when they change from juveniles to adults.
Examples of animals that undergo this process are frogs, toads, midges, moths and butterflies.
· Two kinds of metamorphosis are complete and incomplete.
· A complete metamorphosis has four stages: egg, larva, pupa and adult, eg. Silkworm, bettle and butterfly as well as Frog .
· An incomplete metamorphosis has three stages: egg, nymph and adult eg. Cockroach.
Part E: Fertilisation is necessary for Sexual Reproduction
· In sexual reproduction, two parents donate genes to their young, resulting in offspring with a mix of inherited genes.
· These genes are donated through a process called fertilisation. Fertilisation is defined as the moment when a sperm and egg join together and form a zygote (fertilised egg), it consists of both genes (DNA) from mum and dad, will develop into a new individual.
· There are two mechanisms by which fertilisation can take place.
o External fertilisation - the eggs are fertilised outside of the body
o Internal fertilisation - the eggs are fertilised within the female reproductive tract.
· For fertilisation to occur during reproduction in species, three key requirements must be met:
o male and female gametes are produced and mature at the same time
o gametes must meet a watery environment.
o Terrestrial organisms have overcome the problem of fertilisation in a dry environment by using internal fertilisation, that is, fertilisation occurs within the female body. Male gametes are transferred directly into the reproductive tract of the female so the gametes remain in a moist environment.
· Without internal fertilisation organisms could not colonise and live permanently in terrestrial environments. Internal fertilisation means that terrestrial organisms are able to complete the entire reproductive cycle without having to return to an aquatic environment.
Differences between External and Internal Fertilisation
Internal Fertilisation / External FertilisationWhat is it? / Sperm meets the egg while the egg is still inside the female body / Sperm (male) meets the egg (female) while the egg is outside the female body
Conditions? / Need to have protection for the developing egg / Usually happens in wet environment. Male and female releases their gametes (cells for reproduction) into their surrounding
Advantages? / Protection for the embryo ( the developing young) as it develops within the mother / Usually result in production of large number of offspring
Disadvantages? / Limited number of young / The presence of predators reduces the survival of the eggs
EXAMPLES / Mostly reptiles and mammals / Mostly amphibians and fish. However, not for fish like guppies that give birth.
PART F: SEXUAL REPRODUCTION IN FLOWERING PLANTS
· Sepals protect the flower when it is in bud.
· Brightly coloured and scented petals attract insects for cross-pollination.
· The stamen is the male reproductive organ and it consists of the filament and the anther.
· The filament supports the anther; pollen, which contains the male sex cell, is produced by the anther.
· The female reproductive organ is the pistil and this is divided into the stigma, the style and the ovary.
· The stigma receives the pollen – by wind or animals.
· Pollen grains germinate on the stigma, growing a pollen tube downwards through the style towards the ovary.
· The ovary may contain several ovules, each of which produces an egg.
· When a pollen tube enters an ovule a male nucleus fuses with the female ovum - fertilisation takes place and produce a zygote.
· Each zygote will develop into a seed.
More Information about Reproduction in Flowering plants:
· Pollination is the transfer of pollen from the anther of a stamen to the stigma.
· Fertilisation is the fusion of two gametes; in flowering plants this will be one of the male nuclei from the pollen grain and the ovum inside an ovule of the ovary.
· Pollination can come from the same plant (self-pollination) or other plant (cross-pollination)
· Cross-pollination is preferable over self-pollination because it involves two different parent plants and therefore results in greater variation in the offspring.
· Differences between wind-pollinated flowers and insect-pollinated flowers
Insect Pollinated / Wind Pollinated /large, brightly coloured petals - to attract insects / small petals, often brown or dull green - no need to attract insects
often sweetly scented - to attract insects / no scent - no need to attract insects
usually contain nectar - to attract insects / no nectar - no need to attract insects
moderate quantity of pollen - less wastage than with wind pollination / pollen produced in great quantities - because most does not reach another flower
pollen often sticky or spiky - to stick to insects / pollen very light and smooth - so it can be blown in the wind and stops it clumping together
anthers firm and inside flower - to brush against insects / anthers loosely attached and dangle out - to release pollen into the wind
stigma inside the flower - so that the insect brushes against it / stigma hangs outside the flower - to catch the drifting pollen
stigma has sticky coating - pollen sticks to it / stigma feathery or net like - to catch the drifting pollen
Structure / Function /
Sepals / Green; protect the unopened flower bud
Petals / may be brightly coloured to attract insects
Stamens / the male parts of the flower consisting of the anther held up on the filament
Pistil / The female parts of the flower consisting of the stigma, style and ovary
Anthers / produce male sex cells (pollen grains).
Stigma / the top of the female part of the flower which collects pollen grains
Ovary / produces the female sex cells (ovules)
Nectaries / produce sugary nectar which attracts insects
Pedicel / The flower stalk to support the flower
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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