Reproduction 👉👈

Question 1

Differences between asexual and sexual reproduction

Answer 1

The number of parent organisms (1 : 2)
* How offspring are produced (mitosis or binary fission : meiosis)
* The level of genetic similarity between offspring (genetically identical : genetically unique)
* The possible sources of genetic variation in offspring (only mutation : contribution of 50% of DNA from each parent, meiosis resulting in new combinations of alleles on chromosomes, random distribution of chromosomes during meiosis)
* The number of offspring produced
* The time taken to produce offspring

Question 2

What are the advantages and disadvantages of asexual reproduction

Answer 2

Advantages…
Population increases rapidly when conditions are right
Can exploit suitable environment quickly
Much faster and takes less energy

Disadvantages…
Limited genetic variation (they’re literally clones)
Vulnerable to changes and may only be suitable for one habitat
Disease will affect all

Question 3

What are the advantages and disadvantages of sexual reproduction

Answer 3

Advantages…
Can adapt to different environments
Genetical variation
Less likely to be wiped out by diseases

Disadvantages…
Takes time and effort
Isolated members of species will have difficulty reproducing

Question 4

What are the specific mechanisms leading to genetic variation

Answer 4

Crossing over - the process by which non-sister chromatids exchange alleles during meiosis I
Independent assortment - the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs of chromosomes during meiosis I
Random fertilisation - there are millions of combinations of sperm and egg cells and the fusion of these sperm and egg cell

Question 5

Comparison of male and female gametes

Answer 5

Sperm
* Very small (45um)
*Sperm has head region and flagellum, many structural adaptations
*Capable of locomotion
*Produced every day in huge numbers

Egg
*Large (0.15mm)
*Round cell with few structural adaptations, covered in jelly coating
*Not capable of locomotion
*Thousands of immature egg cells in each ovary, but only one released in each month

Question 6

Function of female reproductive system

Answer 6

Oviduct: Connects ovaries to uterus, lined with ciliated cells to push ovum down. Fertilisation occurs here.
Ovaries: contain ova
Uterus: muscular bag with a soft lining where the fertilisied egg will be implanted to develop into a fetus
Cervix: ring of muscle at the lower end of uterus to keep fetus in place
Vagina: Muscular tube that leads to the inside of the woman’s body, where penis enters during sexual intercourse

Question 7

Function of male reproductive system

Answer 7

Prostate gland and seminal vesicle: Produces fluid called semen that provide cells with nutrients
Sperm duct: sperm passes through here to mix with other fluids
Urethra: tube running down penis to carry out urine or sperm. ring of muscle prevents the two from mixing.
Testis: Contained in scrotum. Produce testosterone and sperm.
Scrotum: Sac supporting testes outside of body to keep sperm lower than body temperture
Penis: Passes urine out of body and and semen into body of a woman
Epididymis: Coiled tubes that store sperm until ejaculation

Question 8

What role does the endometrium play in the process of reproduction?

Answer 8

The endometrium is vital in reproduction as it acts as a nurturing site for a fertilized egg to implant and grow into a fetus. It is a crucial part of the uterus where the embryo attaches, receives nutrients, and develops. The endometrium undergoes changes based on fertilization, either thickening to support the embryo or shedding during menstruation if fertilization does not occur.

Question 9

How does sexual reproduction differ from asexual reproduction in plants and animals?

Answer 9

Sexual reproduction in plants and animals involves the fusion of gametes to produce genetically diverse offspring, while asexual reproduction results in genetically identical offspring without gamete fusion. Plants reproduce sexually through seed formation and asexually through methods like vegetative propagation. Animals reproduce sexually through mating and asexually through processes like budding or fission.

Question 10

Fertilisation in humans steps

Answer 10

• Sperm are released, attracted to oocyte by chemical signals
• When sperm reaches secondary oocyte, the process ongoing in its cell surface prevents more than one sperm from getting in (if not: polyspermy)
• First sperm cell digests its way through the zona pellucida, reaching oocyte cell surface membrane; complementary receptors on the sperm head bind with proteins on the oocyte, allowing gametes to fuse.
• Sperm nucleus remains, sperm flagella and mitochondria destroyed by vesicles from egg
• Enzymes released from cortical granules digest receptor proteins and harden zona pellucida
• Inside egg, there are chromosomes from both gametes in the cytoplasm
• Paternal and maternal gametes form pronucleus where DNA undergoes replication to prepare for mitosis
• The two pronuclei come together, temporary membrane dissolves, diploid cell created = zygote
  *Chromosomes undergo first mitotic division, subsequent divisions take place to form blastocyst

Question 11

Female gametes in plants

Answer 11

-Made in the ovule
-Single diploid cell within the ovule undergoes meiosis to produce 4 daughter cells
-Only one of these daughter cells will survive: undergoes mitosis to produce more female gametes

Question 12

Male gametes in plants

Answer 12

-Found in pollen in the anther
-Released from anther
-Each pollen contains a diploid mothercell which undergoes meiosis to form four haploid pollen grains (gametes)
-Mitosis occurs for more male gametes

Question 13

Job of each part of a plant in fertilisation

Answer 13

Sepal: protects the flower whilst it is still a developing bud
Petal: attracts pollinators
Anther: where male gametes are produced
Pollen: contains male nuclei for fertilisation
Filament: holds anther up
Stigma: part where pollen will land
Style: holds stigma up
Ovary: contains ovules
Ovule: chamber within ovary where female gametes develop

Question 14

Pollination process

Answer 14

Pollination: transfer of pollen from anther to stigma

*After pollination occurs, a pollen tube grows from pollen grain to the style to the ovary
*Male nuclei travel down the pollen tubes to female nuclei. First one will fuse to the ovule nucleus to form a zygote, while the other one will be used as a food store for embryo
*Fertilisation occurs when haploid female and male nuclei fuse and create a diploid zygote
*After, the ovule becomes a seed and the ovary develops into fruit

Question 15

How do insect-pollinated flowers promote cross-pollination?

Answer 15

Petals: large and brightly coloured to attract insects
Scent & Nectar: present - entices insects to visit flower and push past stamen to get to nectar
Number of pollen grains: moderate - insects transfer pollen with a high success rate
Pollen grains: large, sticky or spiky to attach to insects
Anthers: Inside flowers, stiff and firmly attached to brush against insects
Stigma: inside flower, sticky so pollen grains stick to insects

Question 16

How do wind-pollinated flowers promote cross-pollination?

Answer 16

Petals: small, dull, brown or green because no need to waste energy on that
Scent & Nectar: absent - no need to waste energy on that
Number of pollen grains: large - because it’s so random, if there is more there is a greater chance of pollination
Pollen grains: smooth, small, and light to be easy to blow away
Anthers: outside flower, swinging loose on long filaments to release pollen grains easily
Stigma: outside flower, feathery to catch any drifting pollen grains

Question 17

What are the different mechanisms for cross-pollination?

Answer 17

• Different maturation times for pollen and ovules
• Self incompatability:
• Genetic mechanisms to prevent self-pollination like: 1) chemicals so pollen tube won’t grow 2) genes that control growth that inhibit pollen tube
  -Produce only either male or female parts (or whole plant)

Question 18

Requirements for germination

Answer 18

*Water: Seed can swell up, causing seed coat (testa) to burst, allowing growing embryo plant to exit. Water also allows enzymes in embryo to start working so that growth can occur (metabolic activity)
*Oxygen: required for respiration so energy can be released for germination
*Warmth: germination improves as temperature rises (TCE) as reactions which take place are controlled by enzymes, which cannot function effectively when temperature is too low

Question 19

What is the process of germination

Answer 19

*Seed contains plant embryo and food reserves for its growth
*Food reserves contain endosperm tissue which are transferred to embryo through early leaf structures called cotyledons.
*Seeds need to replenish water lost during dormancy and does so through imbibition, which activates biochemistry of embryo
*Rate of transpiration and protein synthesis increases ad the embryo can prepare to emerge through the seed coat
*Structure called radicle is the first to emerge and forms initial root structure which responds to gravity and grows downward into soil
*First structure above ground is called hypocotyl, a curved portion of the plant shoot found bellow the cotyledons growing upward
*As shoot grows the first leaves begin to appear from cotyledons and photosynthesis can begin.