B10 - Reproduction Flashcards
Asexual reproduction
Asexual reproduction does not involve sex cells or fertilisation as only one parent is needed
* defined as a process resulting in genetically identical offspring from one parent
Asexual reproduction in bacteria
Through binary fission:
* Cell contents double so genetic material has replicated
* Cell divides into two by binary fission
* Creating two genetically identical daughter cells
Asexual reproduction in plants (bulbs and tubers)
Through budding
* A short-stemmed bulb which stores the plant’s food can induce budding
* This produces a new plant, a lateral bud which will grow and become genetically identical to the parent plant
Through tubing
* A tuber forms from swollen, fleshy underground stems
* Buds are formed from them
* Seen in potatoes
Asexual reproduction in plants (runners)
- Plants can grow side shoots called runners that contain tiny plantlets on them
- These will grow roots and develop into separate plants which are geneticall identical to the parent
Advantages of asexual reproduction (name 3)
- 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 of asexual reproduction (3)
- Limited genetic variation in population
- 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 not genetic variation
Sexual reproduction
A process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other
Fertilisation
The fusion of gamete nuclei
* resulting in genetic variation in the offspring
Gamete
A sex cell (in animals: sperm and ovum; in plants pollen nucleus and ovum)
Haploid nucleus
Have half the number of chromosomes found in other body cells
* such as gametes: 23 chromosomes
* only contain one copy from each pair of chromosomes
Diploid nucleus
The result of fusion between two haploid nuclei
* such as a zygote
* contains 46 chromosomes all in pairs
Zygote
When the male and female gametes fuse, they become a zygote which is a fertilised egg cell
Advantages of sexual reproduction (3)
- Increases genetic variation
- Species can adapt to new environment due to variation, giving them a survival advantage
- Disease is less likely to affect population
Disadvantages of sexual reproduction (2)
- Takes time and energy to find mates
- Difficult for isolated members of the species to reproduce
Flowers
The reproductive organ of the plant
* usually contain both female and male reproductive parts
Pollen
Produces by plants and contians a haploid nucleus inside that is the male gamete
* they are not capable of locomotion (moving from one place to another
Pollination
The mechanism to transfer pollen from the anther to the stigma
* can be done by insects or by the wind
Flower structure
Sepal
Protect unopened flower
Petals
Brightly coloured in insect-pollinated flowers to attract insects
Anther
Produces and releases the male sex cell (pollen grain)
Stigma
Top of the female part of the flower which collects pollen grains
Ovary
Produces the female sex cell (ovum)
Ovule
Contains the female sex cells (found inside the ovary)
Petals in an insect pollinated flower
Large and brightly coloured to attract insects
Scent and nectar in an insect pollinated flower
Present - entices insects to visit the flower and push past stamen to get to the nectar
Number of pollen grains in an insect pollinated flower
Moderate - insects transfer pollen grains efficiently with a high chance of successful pollination
Size and shape of pollen grains in an insect pollinated flower
Larger, sticky and spiky to attach to insects and be carried away
Anthers in an insect pollinated flower
Inside flower, stiff and firmly attached to brush against insects
Stigma in an insect pollinated flower
Inside flower, sticky so pollen grains stick to it when an insect brushes past
Petals in a wind-pollinated flower
Small and dull, often green or brown in colour
Scent and nectar in a wind-pollinated flower
Absent - no need to waste energy producing these as no need to attract insects
Number of pollen grains in a wind-pollinated flower
Large amount - most pollen grains are not transferred to another flower si the more produced, the better chance of some successful pollination
Shape and size of pollen grains in a wind-pollinated flower
Smooth, small and light so they are easily blown by the wind
Anthers in a wind-pollinated flower
Outside flower, swinging loose on long filaments to release pollen grains easily
Stigma in a wind-pollinated flower
Outside flower, feathery to catch drifting pollen grains
Process of fertilisation in a plant (7 steps)
- Pollen grain lands right on the stigma (of the same species as the flower it came from)
- Pollen grows a pollen tube down the style towards the ovary
- Nucleus inside pollen grain slips down the tube
- The ovary contains one or more ovules which each contain an ovum with a female nucleus that the pollen can fuse with
- Once the nuclei fuse, a zygote is formed
- The zygote will start to divide and eventually form a seed within the ovule
- This seed will be dispersed by wind, water, gravity or other factors
Germination
Germination is the start of growth in the seed
Three factors required for successful germination (and their function)
- Water: allows seed to swell up and the enzymes in the embryo to start working for growth
- Oxygen: so that energy can be released for germination
- Warmth: germination improves with higher temperature (up to optimum) due to enzymes
Agents of pollination (3)
- Animals, including insects
- Wind
- Water
Investigation for germination (set-up)
- Set up 4 boiling tubes, each containing 10 cress seeds on cotton wool
- Tube A: dry cotton wool
- Tube B: moist cotton wool
- Tube C: seeds in boiled and cooled water with a layer of oil on top of it
- Tube D: moist cotton wool
- Leave tubes in set environment for a period of time
- A, B and C incubated at 20 degrees
- D in a fridge at 4 degrees
Investigation for germination (results)
- Tube A - tested for water/moisture
- no germination
- Tube B - tested with all factors present
- germination took place
- Tube C - tested for oxygen
- no germination
- Tube D - tested for temperature
- no germination
Cross-pollination
Occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
Self-pollination
Pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant
Male reproductive system
Female reproductive system
Prostate gland
Produces fluid called semen that provide sperm cells with nutrients
Sperm duct
Sperm passes through the sperm duct to be mixed with fluid produced by the glands before being passed into the urethra for ejaculation
Urethra
Tube running down the centre of the penis that can carry out urine or semen
* ring of muscle in the urethra prevents the urine and semen from mixing
Testis
Contained in a bag of skin (scrotum) and produces sperm (male gamete) and testosterone
Scrotum
Sac supporting testes outside the body to ensure sperm are kept at a temperature slightly lower than body temperature
Penis
Passes urine out of the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse
Oviduct
Connects the ovary to the uterus and is lines with ciliated cells to push the released ovum down it
* fertilisation occurs here
Ovary
Contains ova (female gamates) which will mature and develop when hormones are released
Uterus
Muscular bag with a soft lining where the fertilised egg (zygote) will be implanted to develop into a foetus
Cervix
Ring of muscle at the lower end of the uterus to keep the develoing foetus in place during pregnancy
Vagina
Muscular tube that leads to the inside of the woman’s body
* where the male’s penis will enter during intercourse and sperm are deposited
Adaptations (and reasons) of sperm cells (3)
- Has a flagellum: enables it to swim to the egg
- Contains enzymes in the head region (acrosome): to digest through the jelly coat and cell membrane of an egg cell
- Contains many mitochondria: provide energy from respiration so that the flagellum can move back and forth for locomotion
Adaptations (and reasons) of egg cells (2)
- Cytoplasm containing a store of energy: provides energy for the dividing zygote after fertilisation
- Jelly like coat: forms an impenetrable barrier after fertilisation to prevent other sperm nuclei from entering the egg cell
Compare the size of sperm and egg
- Sperm: very small (45 nano metres)
- Egg: large (0.15 mm)
Compare the structure of sperm and egg
- Sperm: head region and flagellum, many structural adaptations
- Egg: round cell wil few structural adaptations, covered in a jelly coat
Compare the mobility of sperm and egg
- Sperm: capable of locomotion
- Egg: not capable of locomotion
Compare the number of sperm and egg cells
- Sperm: produced every day in huge numbers (about 100 million per day)
- Egg: thousands of immature eggs in each ovary but only one released each month
Describe the growth and development of the fetus (6 steps)
- After fertilisation in oviduct, zygote travels towards the uterus
- This takes about three days during which the zygote will divide several times
- In uterus embryo embeds itself in the thick lining (implantation) and continues to grow and develop
- Major organ development takes place in first 12 weeks during which, emrbyo gets nutrients from mother by diffusion
- Placenta has formed, embryo called fetus
- Gestation takes nine months, rest is growth
Amniotic sac and fluid
The fetus is surrounded by an amniotic sac which contains amniotic fluid (made from the mother’s blood plasma)
* protects the fetus by cuishoning it from bumps
Placenta
Allows diffusion of glucose, oxygen and amino acids from the mother’s blood to the developing foetus for growth
Umbilical cord
The umbilical cord attaches the placenta to the foetus.
* It contains the umbilical artery and the umbilical vein
* The umbilical artery carries urea and carbon dioxide from the foetus to the mother’s blood.
* The umbilical vein carries oxygen and nutrients from the mother’s blood to the foetus.
Secondary sexual characteristics
The changes that occur during puberty as children become adolescents
* controlled by oestrogen and testosterone
Primary sexual characteristics
Present during development in the uterus
* are the differences in reproductive organs etc between males and females
Effects of oestrogen (name 2)
- Breasts develop
- Body hair
- Menstrual cycle begins
- Hips get wider
Effects of testosterone (name 3)
- Growth of penis and testes
- Growth of facial hair and body hair
- Muscles develop
- Voice breaks
- Testes produce sperm
Menstrual cycle, broken down into 3 periods of time
Overall, it is usually 28 days long
* Ovulation: about haflway through the cycle (day 14)
* Egg travels down the oviduct to the uterus
* Menstruation: lasts about 5-7 days and signals the beginning of the new cycle
* occurs if there’s been a failure to fertilise egg so thickenes lining breaks down
* Build up: after menstruation (at about day 7), lining starts to thicken again in preparation for the next egg
STI
Unprotected sexual intercourse can lead to the transfer of pathogens via exchange of body fluids, some are STIs (sexually transmitted diseases)
HIV
An example of an STI is HIV (Human Immunodeficiency Virus), the virus that usually leads to the development of acquired immunodeficiency disease (AIDS)
How is HIV transmitted? (4)
- sharing needles with an infected person
- blood transfusion
- sexual intercourse
- mother to fetus through the placenta or to the baby through breastfeeding
Ways to control the spread of STIs (name 3)
- Limiting the number of sexual partners someone has
- Not having unprotected sex (using a condom)
- Getting tested if unprotected sex or sex with multiple partners has occurred
- Raising awareness through education programs
