16. Reproduction Flashcards
Asexual reproduction
A process resulting in the production of genetically identical offspring from one parent.
Occurs in bacteria.
Genetically identical
Two organisms that have exactly the same gene sequencing, also known as clones.
Offspring
The products of reproduction. New individuals of the same species as the parent(s) that produced them.
How does asexual reproduction occur in bacteria?
The bacterial DNA is copied.
The cell then continues to grow until it splits into two cells.
What are examples of organisms that can reproduce asexually?
- Starfish
- Yeast
- Plants such as ferns + strawberry plant
Asexual reproduction in starfish
Some starfish species can detach an arm –> arm then develops into a full genetic copy of the original.
Asexual reproduction in a strawberry plant
‘Runners’ (vine like extensions) travel from plant and then take root in the soil to produce new young plants.
Advantages of asexual reproduction
- Only one parent is need (saves time and enery in finding a mate) –> speeds up reproduction process
- Occurs very quickly (eg. bacteria = easy to divide)
- In farming crops can be reproduced easily –> no need for seeds
Disadvantages to asexual reproduction
- All individual will have the same characteristics (bc genetically identical)
–> Makes species velnerable to environmental changes (eg. disease)
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.
Gamete
A sex cell, e.g. sperm cell or egg cell.
The nucleus of a gamete is haploid – it contains a single set of unpaired chromosomes.
Male gamete
Sperm cell
Female gamete
Egg cell (ovum or ova plural)
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.
Diploid vs Haploid
Both are a nucleus
Haploid = Contains single set of unpaired chromosomes
Diploid = Contains two sets of chromosomes
Haploid = 23 chromosomes
Diploid = 46 chromosomes
Reproduction - Process (on a cellular level)
Male gamete + female gamete = fuse
Fertilisation = Fusion of gamete nuclei
–> Creates a zygote (eg. fertilised egg cell)
Zygote
Why is offspring not identical to parents in sexual reproduction?
The zygote contains both maternal and paternal DNA.
Organisms using sexual reproduction
- Fungi
- Fish
- Amphibians
- Molluscs
- Birds
- Plants
- Mammals
- Reptiles
- Arthropods
How many chromosomes are there in haploid nueclei?
23 Chromosomes
Only one copy of each chromosome
Advantages of sexual reproduction
- Creates variation within a population –> Population is more resistance to environmental changes + disease.
- Selective breeding bc characteristics are always being introduced to population.
Disadvantages of sexual reproduction
- A lot of time + energy needed to find mate (eg. birds of paradise)
- Sexual reproduction = slower eg. 9 months pregnancy vs bacteria dividing in 20 minutes
16.3 –> Get it done
Reproductive system
The organ system found in animals that is responsible for producing sperm cells or egg cells, and for producing new individuals by sexual reproduction.
Male reproductive system
- Testis
- Scrotum
- Prostate gland
- Sperm duct
- Urethra
- Penis
Testes
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 (in men)
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 reprodutive system
- Ovary
- Oviduct
- Uterus
- Cervix
- Vagina
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
Fertilisation
During sexual intercourse, semen leaves the penis during ejaculation –> Entering the vagina.
Sperm then swims up the vagina, through the cervix, into the uterus + along the oviducts.
Most sperms don’t survive the journey.
After one sperm fertilises the egg, a barrier is formed to prevent other sperms from entering.
Sperm cell - Structure
Three segments = Head, midpiece, flagellum
Head = Acrosome
Midpiece = Mitochondria
Flagellum = Movement
Head of the sperm
Has a structure called the acrosome.
Acrosome secretes digestive enzymes –> allows the sperm cell to pass through the jelly coating on the surface of an egg cell.
Midpiece of the sperm
Contains many mitochondria.
–> Release energy by respiration –> needed to keep the flagellum moving.
Flagellum of the sperm
Part of the sperm cell that can move –> like a tail (propelling the cell from one place to another)
Egg cell - Structure
Nucleus, Cytoplasm, Jelly coat, Follicular cells
Egg cell - Nucleus
Nucleus contains the mother’s DNA (will fuse with the father’s contained in the sperm nucleus)
The egg cell is therefore a haploid.
Egg cell - Cytoplasm
Contains energy stores to allow the egg to surive for several days
+ to nourish the zygote if fertilisation occurs, until it can implant in the wall of the uterus.
Egg cell - Follicular cells
Layer of follicle cells attached to egg helps to nourish the eff during its journey.
Egg cell - Jelly coat
Jell coat allows the sperm to attach.
it then creates a barrier to other sperm cells once on has successfully penetrated it + entered the egg cell.
What happens if two or more sperm cells enter the egg cell?
The zygote doesn’t form / develops incorrectly.
Egg cells vs Sperm cells
Egg cells = 0.1 mm in diameter
Sper cells = 0.05 mm long
Female (usually) releases one egg cell per month
Males can release 40 million - 1.2 billion sperms in a single ejaculation –> increases chance of successful fertilisation
Egg cells can’t move on their own
Sperm cells can use its flagellum to move about at around 1-3 mm per hour.
Embryo
A ball of cells produced by cell division of a zygote.
After about 5 days after fertilisation, the embryo implants into the wall of the uterus –> continuing to divide and grow.
Fetus
Name for an embryo after a certain stage of development (8 weeks in humans).
Complexity of fetus increases as cells become specialised + tissues/organs/organ systems form.
Fetus = surrounded by a protective layer called the amniotic sac, filled with amniotic fluid.
Amniotic sac
A thin sac that protects the developing fetus within the uterus.
- It contains the amniotic fluid
This stops any pathogens (from the mother) from infecting the fetus.
Amniotic fluid
The fluid that surrounds and protects the developing fetus within the amniotic sac.
(The fluid is a shock absorber and stops the fetus from being harmed)
Placenta
Attatched to the wall of the uterus.
- Transfers substances from the mother to the fetus
- Transfers waste substances from the fetus to the mother so her body can excrete them.
Attatched to fetus by a tube called the umbilical cord
Umbilical cord
A cord which connects the fetus to the placenta and contains blood vessels which transport nutrients, oxygen and waste products.
(Also allows the transport of antibodies)
What materials are exchanged through the umbilical cord?
- Placenta provides fetus with the oxygen, carbohydrates, proteins, fats, vitamins,minerals and water needed to grow.
- As it grows the fetus produces waste products (carbon dioxide + urea) –> these substances move between teh placenta + fetus through the umbilical cord.
How are materials exchanged through the umbilical cord?
- Blood supply of the mother doesn’t meet the blood supply of the fetus.
–> Instead substanes diffuse through blood capillaries between the placenta and umbilical cord.
This prevents a barrier to many toxins / pathogens which the mother is exposed to.
Which toxins can cross the placenta and affect the fetus?
Nicotine (eg. from tobacco smoke)
Some pathogens (eg. Rubella virus)
(bacteria can’t cross but some viruses can because bacteria are larger than viruses and can’t cross over the placenta)
Pollination
The transfer of pollen grains from the anther to the stigma.
How plants reproduce by transferring pollen from the male part of the flower to the female part of the flower.
Pollen contains the male gamete
Ovule contains the female gamete
Insect-pollinated
Flowers that transfer their pollen by way of insect pollinators.
Pollinators
Insects that transfer pollen from flower to flower in pollination.
How do insects transmit pollen?
The insects touches the flower (brightly coloured).
Pollen rubs onto the insect.
Insect then moves to another floewr where the pollen rubs onto this new flower.
Flower structure
- Petal
- Sepal
- Ovule
Stamen =
- Filament + Anther
Carpel =
- Stigma + Style + Ovary
Sepal - Description + Function
Green part at the top of the stem, underneath the petals.
To protect the growing flower and help to stop it drying out.
Disappear after pollination
Both wind and insect pollinated plants
Petal - Description + Function
Brightly coloured part of the flower.
To attract insects, birds or mammals to carry out pollination.
Only insect-pollinated flowers not wind-pollinated plants
Stamen - Description + Function
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.
Longer + more visible on wind-pollinated plants
Filament - Description + Function
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.
Both wind and insect pollinated plants
Anther - Description + Function
Coloured, usually with a powdery appearance.
To produce pollen grains, which contain the plant’s male gametes.
On wind-pollinated plants, it is located in the middle so it shakes pollen onto the stigma.
Stigma - Description + Function
Usually green and the tallest part of the inside of the flower, and with a sticky, waxy layer
To trap pollen from other flowers
Hang out in wind-pollinators (so pollen lands on them)
Style - Description + Function
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.
Both wind and insect pollinated plants
Carpel - Description + Function
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
Both wind and insect pollinated plants
Ovary - Description + Function
Green, bulb-shaped part near the bottom of the flower
Contains ovules (which contain the female gametes) which will develop into seeds after fertilisation
Both wind and insect pollinated plants
Ovule - Description + Function
Structures within the ovary.
Female gametes are produced and contained within the ovules. Upon fertilisation, these ovules will develop into seeds.
Both wind and insect pollinated plants
Pollen
Particle that contains the male gametes of a flowering plant.
Insect-pollination
Pollen that is transported by insects has a spiky outer layer.
The spiky outer layer of pollen hooks onto insects so that the pollen can be transported from one flower to another.
Wind-pollinatinon
Flowers that transfer their pollen through the wind.
Pollen that is transported by the wind is smaller, lighter and smoother. (Allows pollen grains to be blown from one flower to another)
Wind-pollinated flowers tend to produce much more pollens than insect-pollinated flowers to increase chance of wind-blown pollen reaching another plant from the same species.
Self-pollination
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-pollination
Transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.
Two types of pollination
Self-pollination
Cross-pollination
Self-pollination - Explained
Self-pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower, or to a different flower on the same plant.
Eg. Peas, Potatoes, Tomatoes
Advantages / disadvantages of self-pollination
Plants do not need to rely solely on pollinators such as insects.
Can grow in areas where pollinators may not live.
Self-pollination reduces variation within a population of plants.
Advantages/ Disadvantages of cross-pollination
- Variation increases (improved ability to respond to changes in the environment + to disease)
Relies of pollinators, eg. wind/ insects/ other animals to transport pollen from one plant to another.
Energy needed to create nectars etc.
Petal - Wind-pollinated vs Insect-pollinated
Wind-pollinated
Small and usually dull in colour because they do not need to attract insects
….
Insect-pollinated
Large and brightly coloured to attract insect pollinators
Anther - Wind-pollinated vs Insect-pollinated
Wind-pollinated
Loosely attached and dangle outside the flower so its pollen can be blown easily by the wind
…
Insect-pollinated
Located inside the flower to brush against insects. Stiff + firm to brush against insect.
Stigma - Wind-pollinated vs Insect-pollinated
Wind-pollinated
Loosely attached and dangle outside the flower so they can catch wind-borne pollen from other plants; often appear feathery
…
Insect-pollinated
Located inside the flower to brush against insects
Nectar
A sweet liquid produced by a flower to attract pollinators.
As insects eat the nectar, they become covered in the flower’s pollen.
Fertilisation in plants
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
Pollen tube
A tube that grows from the pollen grain on the stigma that travels down through the style and into the bottom of the ovary.
How does fertilisation occur in a plant –> Step by step
1) Pollen grain attatches to the stigma.
2) After pollination, a pollen tube begins to grow through the style towards the ovary.
3) Two male gametes, the sperm/pollen, move through this tube.
4) The pollen tube reaches the ovule.
5) The nucleus of one of the two sperm cells fuses with the egg cell (female gamete) nucleus (fertilisation) to form a zygote.
6) 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.
What do seeds need to germinate?
Water
Oxygen
A suitable temperature.
Puberty
The life stage during which bodies change physically and they become able to reproduce.
At what age does puberty occur?
Between the ages 10-16.
Typically occurs at an earlier age for girls than for boys.
Sex hormones
Testosterone = Main male sex hormone
Oestrogen = Main female sex hormone
Testosterone
The main male sex hormone. It plays a key role in the primary and secondary sexual systems in males.
Oestrogen
The main female sex hormone. It plays a major role in the control of the menstrual cycle.
- Inhibits the release of FSH
- Stimulates the release of LH
Secondary sexual characteristics
The characteristics developed during puberty which indicate sexual maturity.
Changes occuring during puberty - Males
- Shoulders widen
- Facial hair grows
- Voice deepens (voice box enlarges)
- Hair under the arms
- Pubic hairs
- Penis and testes grow larger
- Growth spurt
Changes occuring during puberty - Females
- Breasts start to develop
- Hair under the arms
- Pubic hairs
- Hip bones widen
- Menstrual cycle occurs
- Growth spurt
Menstrual cycle
The monthly cycle in which an egg is released from the ovaries, and the lining of the uterus prepares for the possible implantation of a fertilised egg.
If implantation does not happen, the lining breaks down and is discharged from the body, along with the unfertilised egg.
Follicle
One of many such structures found in the ovaries, each with the ability to release an egg cell.
Stages of ovulation
- Egg cells develop within structures called follicles
- Occurs in the middle of a cycle (usually around day 14)
- After ovulation, the follicle develops into a structure called the corpus luteum
Ovulation
The release of a mature egg (ovum) from an ovary; it occurs approximately once every 28 days in humans.
Corpus luteum
The structure that remains after an egg is released from a follicle.
Lining of the uterus - Stages
From day 4 of the menstrual cycle –> lining of the uterus thickens (so egg cell can implant into the lining if the egg cell is fertilised)
If the egg isn’t fertilised, the lining of the uterus will break down again.
Uterus lining discharged from the body through the vagina during menstruation.
FSH
Follicle stimulating hormone. This hormone stimulates the maturation of an egg in the ovaries and the production of oestrogen.
Stimulates the ovary to secrete oestrogen.
Produced in the pituitary gland
LH
Luteinising hormone. This hormone stimulates the release of a mature egg from the ovaries in an event known as ovulation.
Produced in the pituitary gland
Progesterone
A hormone involved in maintaining the lining of the uterus.
- Inhibits the release of FSH and LH
Produced by the corpeus luteum
Four hormones involved in the control of the menstrual cycle + pregnancy.
- Follicle-stimulating hormone ( FSH)
- Luteinising hormone (LH)
- Oestrogen
- Progesterone.
Where are LH and FSH produced?
Produced in pituitary gland (located at the base of the brain)
Where is oestrogen produced?
By the ovary
Where is progesterone produced?
Corpus luteum in an ovary
Pregnancy - Hormones
Placenta takes over production of the menstrual hormones…
Makes sure…
- No more eggs are released from the ovaries
- Maintains a thick uterine lining to support the growing fetus
- Prevents the muscles of the uterus contracting (which would cause the early delivery of a premature baby)
Sexually transmitted infection (STI)
An infection that is transmitted via body fluids through sexual contact.
Can be caused by viruses or bacteria.
Virus - Examples of STI
Genital warts, herpes, HIV
Bacterium - Examples of STI
Chlamydia, gonorrhoea, syphilis
How do you avoid STI’s?
Avoid sexual contact/ use protection
How is HIV/AIDS transmitted?
- By driect contact with certain body fluids from an infected person.
eg.
Blood, semen, vaginal fluid.
Can also be transmitted from motehr to child during childbirth / pregnancy / breast-feeding.
What is HIV/ AIDS
It is a sexually transmitted infection caused by a virus.
AIDS
A sexually transmitted disease caused by the HIV virus. This disease can be fatal and has killed millions of people around the world.
(acquired immune deficiency)
How does the zygote move from the fallopian tube to the uterus?
Through ciliated epithelial cells brushing it.
Implantation
In early development, the zygote forms an embryo which is a ball of cells (blastocyst) that implants into the wall of the uterus.
What happens to hormones during the menstrual cycle? (Step by step)
1- Progesterone levels low → FSH can be released (which causes an egg to mature)
- FSH levels rise → Causes an egg to mature + stimulates release of oestrogen.
- Levels of oestrogen rises → Inhibits release of FSH (prevent more than one egg maturing at a time)
- Levels of oestrogen rises → Stimulates release of LH
- High levels of LH → Causes release of mature egg from follicle (ovulation at about day 14 in cycle)
- Empty follicle / corpus luteum produces progesterone. → Inhibits release of FSH and LH.
- Progesterone + oestrogen maintains uterus lining.
- If the woman doesn’t become pregnant → Falling levels of progesterone + oestrogen trigger menstruation.
- (Falling progesterone → Stimulates release of FSH → New egg begins maturing)
Overview of the interactions between hormones…
FSH - Stimulates the ovary to secrete oestrogen
(This is because the FSH causes an egg to mature → Meaning the uterine lining has to begin developing/being maintained to allow for ovulation)
Oestrogen - Inhibits the release of FSH + Stimulates the release of LH
(This is because oestrogen maintains the uterus lining → meaning another egg doesn’t have to be produced → Also as the uterine lining is ‘maintained’ ovulation can occur)
Progesterone - Inhibits the release of FSH and LH
(This is because the egg cannot begin to mature yet as the corpus luteum is still present. Furthermore, as ovulation has already occurred, there is no need for LH to stimulate ovulation.)
Pollen grains - Wind vs insect pollinated
Wind-pollinators
Smooth + light to get carried in wind.
Large number of pollen grains in wind.
Insect-pollinators
Hooks / sticky to attatch to insects.
