Reproduction & Inheritance Flashcards
What is sexual reproduction ?
he process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other
What are Gametes and zygotes?
A gamete is a sex cell (in animals: sperm and ovum; in plants: pollen nucleus and ovum)
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
This is because they only contain one copy of each chromosome, rather than the two copies found in other body cells
In human beings, a normal body cell contains 46 chromosomes but each gamete contains 23 chromosomes
When the male and female gametes fuse, they become a zygote (fertilised egg cell)
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 advantages and disadvantages of sexual reproduction?
Although there are some clear advantages of sexual reproduction (in comparison to asexual reproduction), there are also a few disadvantages of sexual reproduction
What is Asexual reproduction ?
Asexual reproduction is:
The process resulting in genetically identical offspring being produced from one parent
Asexual reproduction does not involve gametes or fertilisation
Only one parent is required so there is no fusion of gametes and no mixing of genetic information
As a result, the offspring are genetically identical to the parent and to each other (they are clones)
Many plants reproduce via asexual reproduction
Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission
What are advantages and disadvantages of asexual reproduction?
Whilst asexual reproduction has several advantages over sexual reproduction, it also has a few disadvantages
Compare Sexual & Asexual Reproduction?
What is the flower structure ?
What is the description of the flower structure ?
What is pollination ?
Plants produce pollen, which contains a nucleus inside that is the male gamete
Pollination is when pollen is transferred from the anthers of a flower to the stigma.
What is Cross-pollination?
when pollen is transferred from a different flower
What is Self-pollination?
when pollen is transferred from the same flower
What are the 2 main mechanisms by which pollination occurs ?
Insect-pollination: where the pollen is transferred by insects (or sometimes other animals like birds or bats)
Wind-pollination: where the pollen is transferred by the wind
The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function
What are Insect-pollinated flowers?
For the flowers of many plant species, the pollinating agents are insects (e.g. bees)
Insects often visit these flowers to collect nectar (a sugary substance produced by insect-pollinated flowers and the base of their petals, which provides the insects with energy)
As an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect’s body
When the insect visits another flower, it may brush against the stigma of this second flower and in the process, may deposit some of the pollen from the first flower, resulting in pollination
The structures of an insect-pollinated flower ensure that the flower is well-adapted for pollination by insects
What are Wind-pollinated flowers?
For wind-pollinated flowers, the process of pollination is more random than it is for insect-pollinated flowers
When ripe, the anthers open and shed their pollen into the open air
The pollen is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination
The structures of a wind-pollinated flower ensure that the flower is well-adapted for pollination by the wind
What is fertilisation in plants ?
In plants, the ovary contains one or more ovules
The ovules are the structures that eventually develop into seeds
Each ovule contains an ovum
An ovum is an egg cell that contains the female nucleus that a male pollen nucleus can fuse with
In plants, fertilisation occurs when the pollen grain nucleus fuses with the ovum nucleus
What is the growth of the pollen tube ?
Unlike the male gametes in animals (sperm), the pollen grain has no ‘tail’ to swim to the ovary of the flower
Instead, in order to reach the ovum nucleus, the pollen grain grows 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)
The nucleus inside the pollen grain moves down the tube as the tube grows down the style towards the ovary (which contains the ovule that, in turn, contains the ovum)
Once the nucleus of the pollen grain and the nucleus of the ovum have fused (joined together), that particular ovule has been fertilised and a zygote has been formed
The zygote will then start to divide (it is the structure that eventually develops into an embryo plant)
What is Seed and fruit formation?
After fertilisation, the ovule (that contains the zygote) develops into the seed
The wall of the ovule develops into the seed coat, known as the testa
The parts of the flower surrounding the ovule (mainly the ovary walls) develop into the fruit, which contains the seeds
The fruit provides a mechanism for seed dispersal (getting the seeds away from the parent plant)
Some fruits are eaten by animals, which then disperse the seeds in their droppings (the tough outer coat of seeds stops them from being digested)
Some other fruits have sticky hooks that get caught in the fur of passing animals
As different plants have different numbers of ovules, this explains why different fruits have different numbers of seeds (which develop from the ovules)
What are gametes ?
Gametes are sex cells produced by meiosis
What are the sex cells in animal ?
The sperm and ovum in animals
What are the sex cells in plants ?
The pollen nucleus and ovum in plants
Draw a diagram of the human gametes diagram ?
What is fertilisation ?
the fusion of a male and female gamete to produce a zygote
. The zygote then divides by mitosis to develop into an embryo
.Cells start to become specialised to perform specific functions, forming all the body tissues of the offspring
What is fertilisation in humans ?
During sexual intercourse, semen is ejaculated into the female’s vagina near the cervix, and sperm travel through the cervix into the uterus.
Fertilisation occurs in the oviduct if a sperm meets an egg, typically 1-2 days after ovulation
A human zygote contains the full 46 chromosomes (23 pairs of chromosomes)
half of which came from the father and half from the mother
What is fertilisation in plants ?
In plants, fertilisation occurs when a pollen tube grows down from a pollen grain to deliver the male nucleus into the ovary
Here the male and female gametes fuse to form the embryo
What are insect-pollinated flowers ?
- Flowers are the reproductive organs of plants
- The role of flowers is to enable plant gametes to come together in fertilisation
-The male gametes of plants are found in pollen grains
-The female gametes of plants are in ovules
-The process by which pollen is transferred from the male part of a flower to the female part of a flower is known as pollination; this can be carried out in various ways, e.g. by insects or by wind
What are insect pollinated flowers adaptations to attract insects and aid insect pollination ?
What are the structural adaptations of insect-pollinated flowers?
Insect pollinated flowers are adapted to allow insects to collect pollen from one flower and easily transfer it to another flower
When an insect enters a flower in search of nectar it brushes against the anthers, which deposit sticky pollen onto the insect’s body
When the insect visits another flower it brushes against the stigma and deposits some of the pollen from the first flower; this is pollination
Label a wind pollinated flower structure .
Wind-pollinated flowers do not need to attract insects, so their structure differs from that of insect-pollinated flowers
What are structural adaptations of wind pollinated flowers .
Wind pollinated flowers are adapted so that wind can easily catch pollen grains and carry them to the stigmas of other flowers
The anthers and stigmas of wind pollinated flowers hang outside the flower so that:
pollen can easily be blown away by the wind
pollen can easily be caught by the stigmas of other flowers
How does seed a fruit formation take place ?
After fertilisation the ovule develops into a seed
The parts of the flower surrounding the ovule develop into a fruit, which contains the seeds
Fruits provide a mechanism for seed dispersal, e.g.
some fruits are eaten by animals, which then disperse the seeds in their droppings
some fruits have sticky hooks that get caught in the fur of passing animals
What is the difference between pollination and fertilisation in plants ?
Pollination = pollen landing on the stigma of a flower
Fertilisation = fusion of the male and female nuclei
What is germination ?
Germination marks the beginning of seed growth
What are 3 key factors for successful germination ?
Water: swells the seed, breaks the seed coat, and activates enzymes for growth
Oxygen: necessary for respiration to provide energy
Warmth: boosts enzyme activity and improves germination until a certain temperature
Carbon dioxide has no effect on germination
What is the apparatus needed for the practical on conditions of germination ?
Test tubes
Test tube holder
Cress seeds
Cotton wool
Fridge
What is the method for the practical on conditions of germination ?
Prepare 4 test tubes with 10 cress seeds on cotton wool, labeled A, B, C, and D
Tube A: Keep the cotton wool dry
Tube B: Moisten the cotton wool with water
Tube C: Cover the seeds and cotton wool with water and add a layer of oil on top
Tube D: Moisten the cotton wool and place the tube in a fridge (~4°C)
Keep tubes A, B, and C at room temperature or around 20°C
After 3-5 days, ensure the cotton wool in tubes B and D stays moist
Compare the number of germinated seeds in each tube
Draw a table stating the conditions needed for germination .
Is germination the beginning of seed growth ?
Germination is the beginning of seed growth
The seed contains a zygote that develops into the embryo
During germination, the embryo grows into a seedling
Cotyledons surround the embryo, storing food for the seedling
Some plants have one cotyledon, others have two
Cotyledons provide energy until the plant can photosynthesize
Water absorption splits the seed coat (testa), allowing the plumule (first emerging shoot) and radicle (first emerging root) to emerge
What are plant runners ?
Some plants grow side branches, known as runners, that have small plantlets at their ends
Runners are horizontal stems that grow sideways out of the parent plant
Once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant
What are Artificial asexual reproduction in plants – cuttings?
A simple method to clone plants (mainly used by gardeners) is by taking cuttings
This is an artificial method of asexual reproduction
The method for taking cuttings is as follows:
Gardeners take cuttings from good parent plants (i.e. those that are healthiest and best-looking)
A section of the parent plant with a new bud is cut off
This cutting can either be placed into water until new roots grow or can sometimes be placed directly into soil
Sometimes, the stem of the cutting may first be dipped into ‘rooting powder’, which contains plant growth regulators (rooting hormones) that encourage new root growth
These cuttings are then planted and eventually grow into adult plants that are genetically identical to the original plant
Plants cloned by taking cuttings can be produced cheaply and quickly
What are the female reproductive system ?
The female reproductive system consists of several key components:
Oviducts: Connects ovary to the uterus, lined with ciliated cells to push released ovum, fertilisation occurs here
Ovaries: Contains ova (female gametes) that mature and develop when hormones are released
Uterus: Muscular bag with soft lining where fertilised egg (zygote) implants to develop into foetus
Cervix: Ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy
Vagina: Muscular tube leading to inside of woman’s body, where male’s penis enters and sperm are deposited during intercourse
What happens during the menstrual cycle ?
Draw a menstrual cycle graph.
What is the interaction between all four of the menstrual cycle hormones
The pituitary gland releases FSH to develop an ovarian follicle
The follicle produces an egg and oestrogen
Oestrogen stimulates uterine lining growth and inhibits FSH production
High oestrogen levels trigger LH release from the pituitary, causing ovulation (around day 14)
The follicle becomes the corpus luteum, producing progesterone
Progesterone maintains the uterine lining
If the egg isn’t fertilised, the corpus luteum breaks down, progesterone levels drop, and menstruation occurs
If pregnant, the corpus luteum continues producing progesterone until the placenta develops, which then maintains progesterone production throughout pregnancy
Label the pregnancy ?
What does the placenta contain ?
Contains both maternal and foetal blood.
The maternal and foetal blood NEVER MIX.
What are some substances that are exchanged across the placenta ?
What are the female secondary sexual characteristics ?
What are the male secondary sexual characteristics ?
Where a genes located ?
Genes are found in specific locations on the chromosomes, these locations were identified in the human genome project
What are the four different types of nucleotide bases?
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
The bases are bonded together by complementary base pairing
A pairs with T
G pairs with C
What are the examples of an RNA molecules ?
messenger RNA (mRNA) which is the transcript copy of a gene that encodes a specific polypeptide
transfer RNA (tRNA) which is involved in protein synthesis
ribosomal RNA (rRNA) which forms part of a ribosome
