Reproduction

what is sexual reproduction definition

The production of genetically different offspring resulting from two parents, each producing gametes which fuse in a process called fertilisation

what is asexual reproduction definition

The production of offspring that are genetically identical to the parent

what are advantages of sexual reproduction

• Creates a genetic diversity within a species, leading to higher levels of disease resistance and a greater ability to adapt to changing conditions

• Combination of chromosomes from two organisms increases variation, which assists with survival

Genetic variation from recombination of genes increases the chances of survival under changing conditions.

Greater evolutionary potential — more likely to develop beneficial adaptations.

what are disadvantages of sexual reproduction

• Can prevent favourable genes from being passed to offspring (if it’s a recessive gene), which is not possible for an isolated organism.

• Requires mating of two organisms which is dependent on syncing ferility cycles, and the production of offspring is slower and less prolific than sexual reproduction

Slower and more energy-intensive.

Requires finding a mate.

Not always successful (e.g., unsuccessful fertilisation or offspring may not survive).

what are advantages of asexual reproduction

• Offspring are clones of parents, meaning favourable traits are effectively passed through generations. It is also less energy intensive than sexual reproduction, meaning the population can increase rapidly and exploit suitable habitats quickly.

Fast and efficient (e.g., binary fission, budding, vegetative propagation).

No need for a mate — useful in isolated or low-density environments.

Offspring are clones — successful traits are passed on unchanged.

what are disadvantages of asexual reproduction

Pathogens may spread easily from parent to offspring. This reduction in genetic diversity increases the susceptibility to species to new diseases, and evolution is reduced due to the lack of genetic variation.

Lack of genetic variation — all offspring are genetically identical, making the population vulnerable to disease and environmental change.

Evolutionary disadvantage — reduced ability to adapt to new or changing environments

what does sexual reproduction mean

• Animals undergo sexual reproduction which means:

• Gametes are produced by parent organisms through meiosis

• Each gamete contains half the necessary number of chromosomes

• The male gamete (sperm) fertilises the female gamete (ovum or egg) by either internal fertilisation (mammals) or external fertilisation (fish such as salmon)

• Fusion of gametes results in production of a zygote, which contains a combination of genetic material from both parental organisms

what is external fertilisation

- The egg is fertilised outside the females body.

- Many of the male and females gametes are released into their surroundings where some fuse together, forming a zygote 

- Usually requires water or moist environment because it keeps gametes from drying out

   Examples: amphibians, fish, coral

what are advantages of external reproduction

• It does not place great energy demand on the organism in terms of parental care or time spent looking for a mate 

• Once the gametes have fused to produce a zygote, the offspring can disperse easily to colonise new area, this 

→ reduces competition for food, space

→ increases survival of offspring by spreading away from predators

what are disadvantages of external fertilisation

• As the gametes are released directly into the surrounding environment, they may be eaten by waiting predators

  o    E.g fish to coral spawning 

• In aquatic environments, the currents may sweep away the gametes, preventing fertilisation - may be counteracted by producing and releasing many at once

• When there is no close contact between organisms, timing the release of gametes to ensure fertilization is crucial

what is internal fertilisation

- Eggs are fertilised by sperm inside the female’s body 

- It is practiced by species that lay shelled eggs or have a period of embryonic development 

- To take place, the male and female must be in a close proximity to one another. The male often has a copulatory organ for delivering sperm to the reproductive tract of the female

what are advantages of internal fertilisation

·       There is a high probability of successful fertilisation unlike external fertilization 

·       There Is protection from external threats e.g predators, currents 

·       Less gametes need to be produced by the males and females which means that there is a reduced energy cost on organisms 

·       An external water source is not required -> fluid in the females reproductive tract allows the sperm to swim and fuse to the egg

what are disadvantages of internal fertilisation

·       the organism needs to be proximity from one another, there are great energy demands on both males and females to find a mate

·       One parent must carry and protect the offspring until they are old enough to fend for themselves 

Due to the large costs involved with caring for offspring during the gestation period, as well as the limited space offered by internal reproductive tracts, few offspring can be produced via internal fertilisation.

what are asexual methods which animals use

Budding, Fragmentation and pathogenesis

whats the process of sexual reproduction in plants

·   Flowers are the reproductive organs of sexually reproducing plants, offspring are produced by the fusion of two haploid gametes.

·   Male gametes (pollen) are produced and transferred to the female ovules.

·   This process is called pollination, and can be assisted by wind or insects.

·   After pollinations, fertilisation occurs and the ovules grow into seeds in a fruit, which disperse once ripe.

·   The seed is then freed from the fruit

what is pollination

Pollination is the transfer of pollen (male gamete) from the anther (part of the stamen) to the stigma (part of the carpel) of a flower.

Self-pollination: Pollen is transferred within the same flower or between flowers on the same plant.

Cross-pollination: Pollen is transferred between different plants of the same species.

what is fertilisation

Fertilisation is the fusion of male and female gametes to form a zygote.

Steps involved:

1. After pollination, the pollen grain lands on the stigma and germinates, forming a pollen tube.

2. The pollen tube grows down through the style toward the ovary.

3. The male gametes (sperm nuclei) travel down the pollen tube.

One sperm nucleus fuses with the ovule’s egg cell, forming a zygote, which will develop into the embryo.

identify ways by which pollination can occur

Wind: The flowers anthers are very long and produce large amounts of smooth, light pollen, which is easily picked up by the wind passing over the flowers

Vector: An animal can pick up the pollen and then seek and find the next individual flower of that species and carry the pollen to it.  visual and olfactory cues

identify ways in which seed disperal can occur

Seed dispersal: is the process by which seeds are spread away from the parent plant to reduce competition and increase the chances of survival and germination in new locations.

Water Dispersal: They produce light seeds which float, or there may be fluff that helps buoyancy 

Trees found on tropical beaches have their seeds carried by the seed 

Animal dispersal: Hook, spikes, and spines attaching to fur  some eat the seeds and pass through the gut

what is the asexual reproduction in plants

Structural modifications to the stems or roots of the plant results in the production of new individuals, without the need for production of seeds or spores

why might plants find this form of reproduction advantageous

1.     if the environment has been stable for many generations, variability may not be essential to the survival of the species 

2.     It is not as complex and requires far less energy 

3.     When colonizing a new area, finding a mate for sexual reproduction may be difficult or impossible

If the environment is harsh, the more delicate organs of sexual reproduction may not be able to survive 

what are examples of asexual reproduction in plants

Runners

• long, slender stems grow on the surface of the soil 

• In Strawberries leaves, flowers and roots are produced at every other node on the runner. Just beyond each second node, the tip of the runner turns up and becomes thickened. This thickened position fortune first produces adventitous roots and then a new shoot that continues the runner 

  E.g native australian violets 

Vegetative propagation

-        Where if a piece of the plant is cut and replated it will sustain itself 

-        Includes growing cuttings 

Example : frangipani 

How does Fungi sexually reproduce

Plasmogamy: two genetically different cells fuse together

Karyogamy: the nuclei fuse

Meiosis: gametes are generated which produces spores that are distributed into the environment

How does Fungi asexually reproduce

Budding: Fungus develops a growth that then breaks off to form a new organism 

Spores: Sex cells are released directly into the surrounding environment to spread and grow elsewhere. 

when does fungi asexually reproduce

Reproduces asexually when environmental conditions are favourable, meaning there are ample nutrients and a stable environment, allowing them to rapidly spread by producing large numbers of genetically identical spores through asexual reproduction; this is often the default method when conditions are ideal.

how does bacteria reproduce

-        Only reproduce asexually

-        Bacteria tend to have a short life cycle so they rapidly increase population size

It only requires a single organism in order to produce offspring

• through binary fission

How does protists reproduce?

Asexually

• Binary fission: where a single cell divides into two identical daughter cells

• Budding: A small outgrowth, called a "bud," develops on the parent cell, which then grows and eventually detaches to become a new, independent organism, essentially creating a clone of the parent cell; this process involves a portion of the parent cell's cytoplasm and nucleus being separated to form the bud. 

describe the process of sexual reproduction in humans

Sexual reproduction begins with development of gametes. In females this occurs in the ovaries, where ovum (eggs) are produced and released into the fallopian tubes. There is a 12–24-hour window after release called ovulation, during which fertilisation the fusion of an egg and a sperm cell can be successful. Once fertilisation has occurred the zygote begins to divide and migrate from the fallopian tube into the uterus. Here, the now blastocyst embeds itself into the walls of the uterus called the endometrium. This is a nutrient dense lining which will provide oxygen and nutrients to the growing embryo. This occurs about seven days after fertilisation establishing the pregnancy

define fertilisation

the fusion of gametes to initiate the development of a new organism

define seamen

a fluid containing spermatozoa and other secretions to transport, sustain and protect the male gametes 

define oocyte

an immature female germ cell that gives rise to the ovum or female gamete containing a haploid set of chromosomes and food reserves 

what are the steps for fertilisation

1.     Ovulation → ovary releases the egg – the ovum (eggs) are produced and released into the fallopian tubes, there is a 12-24 hour window

2.     Egg travels through fallopian tube 

3.     Male release semen (containing sperm) during sex into the vagina to swim through to the cervix and uterus before finally making it to the oviduct where the egg is waiting 

4.     Egg and sperm fuse together to form the first complete cell of the new organism → the zygote (fertilised egg)

5.     The zygote will make the journey down the oviduct to the uterus

what are the conditions for fertilisation

1.     Both male and female gametes need to be produced and ready at the same time 

2.     Arrangements need to be made to bring the gametes in close contact with one another 

3.     Water needs to be present (male gametes must swim to the female gamete without drying out)

define implantation

when a fertilised egg adheres to the wall of the uterus

what is the process of implantation

1.     Fertilisation occurs in the fallopian tube, forming a zygote.

2.     The zygote undergoes mitotic divisions (cleavage) as it travels to the uterus, forming a blastocyst.

3.     Around 5–7 days after fertilisation, the blastocyst reaches the uterus.

4.     The blastocyst attaches to the endometrium, usually in the upper part of the uterus.

5.     The outer layer of the blastocyst (called the trophoblast) begins to invade the uterine lining and form part of the placenta.

The endometrium thickens and becomes more vascularised (rich in blood vessels) to support the developing embryo.

what are the key hormones is control of pregnancy

1. Human chorionic gonadotrophin

2. Progesterone

3. oestrogen

what is Human Chorionic Gonadotrotrpin

·       HCG is produced by a tissue in the early embryo which will later become the placenta

·       Responsible for thickening the lining of the uterus so that it can hold a growing embryo, by triggering your body to release more oestrogen and progesterone which will also tell your body to cease menstruation.

·       It supports the function of the corpus luteum, a temporary structure in the ovaries essential in early pregnancy.

It's also the hormone detected by pregnancy tests.

what is progesterone

·       It is first produced in the corpus luteum after ovulation, then by the placenta.

·       Helps to strengthen the uterine lining for the incoming pregnancy, then encourages glands in the endometrium to provide nutrients for the growing embryo.

·       It stimulates growth of blood vessels that supply the womb and inhibits contraction of the uterus so it grows as the baby does.

·       strengthens pelvic wall muscles for labour. 

·       It helps the mothers immune system tolerate the infant 

Relaxes uterine muscles and strengthens pelvic floor muscles so you don’t go into early labour

what is oestrogen

·       Helps the growth and thickening oof the uterine lining in the early stages of pregnancy.

·       Assists foetal organs develop.

·       Activates and regulates production of other hormones.

·       With progesterone, stimulates breast growth and milk duct development.

what is the positive feedback loop of oxytocin during labour

Oxytocin role: ejection of milk whilst breastfeeding and maternal bonding. Initiates and strengthens rhythmic uterine contractions. 

-        In the initiation of labour estrogen levels rise white progesterone levels fall and uterine contractions begin. The placenta releases prostaglandins and oxytocin is released by the pituitary. Combination of these hormones produce contractions