16 Reproduction Flashcards
Asexual reproduction
A process resulting in the production of genetically identical offspring from one parent.
Organisms that can reproduce asexually include:
Bacteria
the starfish
yeast (a single-celled fungus)
many plants such as ferns and the strawberry plant
Advantages and disadvantages of asexual reproduction
Advantages
The population can be increased rapidly when conditions are right
Can exploit suitable environments quickly
More time and energy-efficient
Reproduction is completed much faster than sexual reproduction
Disadvantages
Limited genetic variation in population - offspring are genetically identical to their parents
The population is vulnerable to changes in conditions and may only be suited for one habitat
Disease is likely to affect the whole population as there is no genetic variation
Sexual reproduction
A process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote, and the production of offspring that are genetically different from each other.
Fusion
The process of joining or fusing together two nuclei during sexual reproduction.
Fertilisation
The fusion of gamete nuclei to form a zygote.
Zygote
A cell produced by the fusion of the nuclei from two gametes during fertilisation. The nucleus of a zygote is diploid – it contains two sets of chromosomes.
Halpoid
Describes a nucleus containing a single set of unpaired chromosomes.
Diploid
Describes a nucleus containing two sets of chromosomes, for example in body cells.
Advantages and disadvantages of sexual reproduction
Advantages
Increases genetic variation Takes time and energy to find mates
The species can adapt to new environments due to variation, giving them a survival advantage
Disease is less likely to affect the population (due to variation)
Disadvantages
Difficult for isolated members of the species to reproduce
Takes time and energy to find mates
Pollination
The transfer of pollen grains from the anther to the stigma.
Flower male parts
Sepal: green part at the top of the stem, underneath the petals. To protect the growing flower and help to stop it drying out
Petal: brightly coloured part of the flower to attract insects, birds or mammals to carry out pollination
Stamen: the male part of the flower consisting of the filament and the anther. To produce male gametes (pollen) and provide the correct structures and conditions necessary for the transfer of pollen
Filament: the stalk that supports the anther. To hold the anther in a position where it is able to transfer its pollen to an insect, mammal or bird
Anther: coloured, usually with a powdery appearance to produce pollen grains, which contain the plant’s male gametes
Flower female parts
Stigma:usually green and the tallest part of the inside of the flower, and with a sticky, waxy layer to trap pollen from other flowers
Style: the thin structure that supports the stigma and is above the ovary,to support and present the stigma in a position where it can receive pollen from an insect, bird or mammal
Carpel: the female part of the flower that contains the stigma, style and ovary to produce female gametes and provide the correct structures and conditions necessary for fertilisation
Ovary: green, bulb-shaped part near the bottom of the flower, contains ovules (which contain the female gametes) which will develop into seeds after fertilisation
Ovule: structures within the ovary, female gametes are produced and contained within the ovules. Upon fertilisation, these ovules will develop into seeds
Pollen for insects and for wind
Insects:
The spiky outer layer hooks onto insects so that the pollen can be transported from one flower to another
Wind:
Pollen that is transported by the wind is smaller, lighter and smoother. This allows the pollen grains to be blown from one flower to another.
Plants produce millions of pollen grains, but wind-pollinated flowers tend to produce much more pollen than insect-pollinated flowers. This increases the chance of wind-blown pollen reaching another plant from the same species.
Self and cross-pollination
Self
The transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant.
Cross
Transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.
Structure of flower wind, insect
Wind-pollinated flower:
Petal: small and usually dull in colour because they do not need to attract insects
Anther: loosely attached and dangle outside the flower so its pollen can be blown easily by the wind
Stigma: loosely attached and dangle outside the flower so they can catch wind-borne pollen from other plants; often appear feathery
Insect-pollinated flower
Petal: large and brightly coloured to attract insect pollinators
Anther: located inside the flower to brush against insects
Stigma: located inside the flower to brush against insects
Nectar to attract insects
Fertilisation in plant
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule
After pollination, a pollen tube begins to grow through the style towards the ovary.
Two male gametes, the sperm, move through this tube. Eventually the pollen tube reaches the ovule. The nucleus of one of the two sperm cells fuses with the egg cell (female gamete) nucleus (fertilisation) to form a zygote .
The zygote develops into an embryo, which eventually becomes the new plant.
Germination
The process, controlled by enzymes, in which the seed begins to develop into a new young plant.
To germinate, most seeds need:
water
oxygen
a suitable temperature.
Male reproduction system
Testis: organ in which sperm cells and testosterone are produced
Scrotum: sack of skin that contains the testes, helping to keep them at a slightly lower temperature than the rest of the body
Prostate gland: secretes fluid that nourishes and protects the sperm; the mixture of liquid and sperm is known as semen
Sperm duct: muscular tube that connects a testis to the urethra
Urethra: tube that allows the passage of semen and urine through the centre of the penis
Penis: during sexual intercourse, the penis is inserted into the vagina, allowing the sperm to transfer into the female reproductive system
Female reproductive system
Ovary: produces egg cells, and the hormones oestrogen and progesterone
Oviduct: tube connecting an ovary to the uterus; fertilisation usually occurs here
Uterus: organ in which the embryo develops
Cervix: ring of muscle between the vagina and the uterus
Vagina: elastic muscular canal through which the newborn passes during childbirth; during sexual intercourse, the male’s penis is inserted into the vagina
Sperm cells
The tip of the head has a structure called the acrosome. This secretes digestive enzymes that allow the sperm cell to pass through the jelly coating on the surface of an egg cell.
The flagellum is the part of the sperm cell that can move, rather like a tail, propelling the cell from one place to another.
The midpiece of the sperm cell contains many mitochondria. These organelles release energy by respiration, which is needed to keep the flagellum moving.
Egg cell
The nucleus contains the mother’s DNA that will fuse with the father’s contained in the sperm’s nucleus.
The cytoplasm contains energy stores to allow the egg to survive for several days and nourish the zygote if fertilisation occurs until it can implant in the uterus wall.
The jelly coat around the egg cell allows the sperm to attach and creates a barrier to other sperm cells once one has successfully penetrated it and entered the egg cell.
The layer of follicle cells attached to the egg helps to nourish the egg during its journey.
SEX
During sexual intercourse for reproduction, a man places his erect penis into a woman’s vagina.
Eventually, semen leaves the penis during ejaculation and enters the vagina.
Sperm in the semen then attempt to swim up the vagina, through the cervix, into the uterus and along the oviducts.
However, the majority of the sperm will not survive the journey.
A few may make it far enough to come into contact with the egg, but only one will be able to fertilise it as, once the first sperm is successful, a barrier is formed to prevent any more from entering.
Fertilisation is the fusion of the nucleus from a male gamete (sperm) and the nucleus from a female gamete (egg cell) to form a zygote.
Sperm cells and egg cells are adapted to their functions.
Embryo
A ball of cells produced by the cell division of a zygote.
Pregnancy
In early development, the zygote forms a ball of cells called an embryo
Fertilisation and development of the zygote into an embryo.
Around five days after fertilisation, the embryo implants into the wall of the uterus, where it continues to divide and grow.
