16.1. Types of Reproduction Flashcards
What does asexual reproduction NOT require?
Asexual reproduction does not involve sex cells or fertilisation
What does asexual reproduction require?
Only one parent is required
Due to only one parent being required, what is different from sexual reproduction?
there is no fusion of gametes and no mixing of genetic information
What is a similarity between the parent and the offspring in asexual reproduction?
As a result, the offspring are genetically identical to the parent and to each other (clones)
Asexual reproduction defintion
Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent
How do bacteria reproduce?
Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission:
How can plants reproduce asexually?
Plants can reproduce asexually using bulbs and tubers
- by using runners
What are bulbs and tubers?
these are food storage organs from which budding can occur, producing new plants which are genetically identical to the parent plant
What are runners?
Some plants grow side shoots called runners that contain tiny plantlets on them (a good example of this are strawberry plants. These will grow roots and develop into separate plants, again being genetically identical to the parent plant
What are 4 advantages of asexual reproduction?
- population can be increased rapidly when conditions are right
- can exploit suitable environments quickly
- more time and energy efficient
- reproduction completed much faster than sexual reproduction
What are 3 disadvantages of asexual reproduction?
- limited genetic variation in population - offspring are genetically identical to their parents
- 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
When (in what organism) is asexual reproduction particularly advantageous and why?
Specifically in crop plants, asexual reproduction can be advantageous as it means that a plant that has good characteristics (high yield, disease-resistant, hardy) can be made to reproduce asexually and the entire crop will show the same characteristics
sexual reproduction definition
Sexual reproduction is 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 definition
Fertilisation is defined as the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring
What is a gamete?
A gamete is a sex cell
in animals: sperm and ovum; in plants pollen nucleus and ovum
How do gametes differ from normal cells? What is this called?
Gametes differ from normal cells as they contain half the number of chromosomes found in other body cells – we say they have a haploid nucleus
How do gametes only have half the number of chromosomes found in the body?
This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells
How many chromosomes does a normal cell have compared to a gamete?
In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
What is a zygote?
When the male and female gametes fuse, they become a zygote (fertilised egg cell)
How many chromosomes does a zygote have and what is this called?
This contains the full 46 chromosomes, half of which came from the father and half from the mother – we say the zygote has a diploid nucleus
What are 3 advantages of sexual reproduction?
- increases genetic variation
- the species can adapt to new environments due to variation, giving them a survival advantage
- disease is less likely to affect population (due to variation)
What are 2 disadvantages of sexual reproduction?
- takes time and energy to find mates
- difficult for isolates members of the species to reproduce
In what way do most crop plants reproduce and how is this beneficial?
Most crop plants reproduce sexually and this is an advantage as it means variation is increased and a genetic variant may be produced which is better able to cope with weather changes, or produces significantly higher yield
What may be a disadvantage as a result of crop plants reproducing sexually?
The disadvantage is that the variation may lead to offspring that are less successful than the parent plant at growing well or producing a good harvest
What are the reproductive organ of the plant?
flowers
What do flowers contain?
They usually contain both male and female reproductive parts
What do plants produce which acts as the male gamete?
Plants produce pollen which contains a nucleus inside that is the male gamete
What is a difference between pollen and sperm?
Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another)
What is pollination?
plants have to have mechanisms in place to transfer pollen from the anther to the stigma
This process is known as pollination
In what two ways can pollination occur?
here are two main mechanisms by which it occurs: transferred by insects (or other animals like birds) or transferred by wind
Does the structure of insect and wind=pollinated flowers differ?
YES
The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function
Sepal definition
protects unopened flower
petals definition
brightly coloured in insect-pollinated flowers to attract insects
anther definition
produces and releases the male sex cell (pollen grain)
stigma definition
top of the female part of the flower which collects pollen grains
ovary definition
produces the female sex cell (ovum)
ovule definition
contains the female sex cells (found inside the ovary)
How do the petals differ in an insect vs wind pollinated flower?
🦟 - large and brightly coloured to attract insects
🌬 - small and dull, often green or brown in colour
How does the scent and nectar differ in an insect vs wind pollinated flower?
🦟- present - entices insect to visit the flower and push past stamen to get to nectar
🌬 - absent - no need to waste energy producing these as no need to attract insects
How does the number of pollen grains differ in an insect vs wind pollinated flower?
🦟 - moderate - insects transfer pollen grains efficiently with a high chance of successful pollination
🌬 - large amounts - most pollen grains are not transferred to another flower so the more produced, the better the chance of some successful pollination occurring
How do the pollen grains differ in an insect vs wind pollinated flower?
🦟 - larger, sticky and / or spiky to attach to insects and be carried away
🌬 - smooth, small and light so they are easily blown by the wind
How do the anthers differ in an insect vs wind pollinated flower?
🦟 - inside flower, stiff and firmly attached to brush against insects
🌬 - outside flower, swinging loose on long filaments to release pollen grains easily
How does the stigma differ in an insect vs wind pollinated flower?
🦟 - inside flower, sticky so pollen grains stick to it when an insect brushes past
🌬 - outside flower, feathery t catch drifting pollen grains
When does cross-pollination occur?
Cross-pollination occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
Why do most plant carry out cross-pollination?
This is the way most plants carry out pollination as it improves genetic variation
What is self-pollination?
Occasionally, the pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant – this is known as self-pollination
What is a disadvantage of self-pollination?
Self-pollination reduces genetic variety of the offspring as all the gametes come from the same parent (and are therefore genetically identical)
Why is a lack of variation in offspring a disadvantage?
Lack of variation in the offspring is a disadvantage if environmental conditions change, as it is less likely that any offspring will have adaptations that suit the new conditions well
What is a disadvantage of cross-pollination?
On the other hand, cross-pollination relies completely on the presence of pollinators and this can be a problem if those pollinators are missing (eg the reduction in bee numbers is of great importance to humans as bees pollinate a large number of food crops) – this doesn’t apply to wind-pollinated plants
When does fertilisation occur?
Fertilisation occurs when a pollen nucleus fuses with an ovum nucleus in the ovule
How does the pollen travel to the ovary, if it can’t move?
As the pollen has no ‘tail’ to swim to the ovary of a plant, in order to reach the ‘female’ nucleus in the ovary it has to grow a pollen tube
What condition is necessary for the pollen to grow a pollen tube?
This only happens if the pollen grain has landed on the right kind of stigma (i.e. of the same species as the flower the pollen came from)
What happens once the pollen has grown a pollen tube?
The nucleus inside the pollen grain slips down the tube as it grows down the style towards the ovary
What does the ovary contain?
The ovary contains one or more ovules which each contain an ovum with a female nucleus that a male pollen nucleus can fuse with
What happens once the nucleus has travelled down the pollen tube?
the nuclei (pl) have joined together, that ovule has been fertilised and a zygote has been formed
What happens to the zygote in the ovary? (plants)
The zygote will start to divide and eventually form a seed within the ovule
Why do different fruits have different numbers of seeds?
As different plants have different numbers of ovules, this explains why different fruits (which develop from the ovary) have different numbers of seeds (which develop from the ovules)
What is germination?
Germination is the start of growth in the seed
What three factors are required for successful germination?
- water
- oxygen
- warmth
Why is water needed for germination?
allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur
Why is oxygen needed for germination?
so that energy can be released for germination
Why is warmth needed for germination?
germination improves as temperature rises (up to a maximum) as the reactions which take place are controlled by enzymes
What factor does not make a difference for germination?
As carbon dioxide is not necessary for germination but also does not inhibit it, it makes no difference whether it is present or not
How could you set up an experiment to investigate germination?
- Set up 4 boiling tubes each containing 10 cress seeds on cotton wool
- Set each test tube as shown in diagram below
- Leave tubes in set environment for a period of time: A, B and C incubated at 20°C; D placed in a fridge at 4°C
- Compare results and see which tube has the greatest number of germinated seeds
Will a seed germinate if it has 1 factor present e.g oxygen but not any others?
NO - needs all 3 factors
