Reproduction in Plants & Humans (Cambridge (CIE) IGCSE Biology)
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1/54- FrontAsexual Reproduction
Define the term asexual reproduction.
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Define the term asexual reproduction.
Asexual reproduction is the reproductive process that results in genetically identical offspring from one parent.
What are some examples of asexual reproduction in living organisms?
Examples of asexual reproduction in living organisms include:
binary fission in bacteria
plants reproducing via bulbs, tubers or runners
budding in yeast cells
budding in jellyfish
parthenogenesis in aphids
What are the advantages of asexual reproduction for wild populations and crop production? (Extended Tier Only)
Asexual reproduction can be advantageous because it produces offspring that are genetically identical to their parents, meaning that:
characteristics that are well suited to the current environment of a wild population are preserved
desirable characteristics of cultivated crop varieties are preserved
In addition to this, asexual reproduction only requires one parent so energy does not need to be expended to find a mate.
What are the disadvantages of asexual reproduction for wild populations and crop production? (Extended Tier Only)
Asexual reproduction can be disadvantageous because offspring lack genetic variation, meaning that:
wild populations are less able to adapt to environmental change
crop varieties will all be susceptible to the same pests and diseases
Define the term sexual reproduction.
Sexual reproduction is the reproductive process during which the nuclei of two gametes fuse to form a zygote and genetically different offspring are produced.
Define the term fertilisation.
Fertilisation is the fusion of gamete nuclei.
What does it mean when gametes are described as haploid? (Extended Tier Only)
Gametes are haploid, meaning that they contain half the full number of chromosomes.
True or False?
Zygotes are diploid. (Extended Tier Only)
True.
Zygotes form when two haploid gametes fuse, producing a diploid zygote with the full number of chromosomes.
What are the advantages of sexual reproduction for wild populations and crop production? (Extended Tier Only)
Sexual reproduction can be advantageous because it generates genetic variation; this means that:
wild populations can adapt to changes in their environment
crop plants may not all be equally susceptible to pests and disease
What are the disadvantages of sexual reproduction for wild populations and crop production? (Extended Tier Only)
Sexual reproduction can be disadvantageous because offspring are different to their parents, meaning that:
some of the offspring in a wild population may be less well suited to their environment than their parents
the desirable traits of a crop may not be present in offspring grown from seed
What are the structures labelled A-D in the diagram?
Structures A-D are:
A = anther
B = style
C = stigma
D = ovary
True or False?
Petals of insect-pollinated flowers tend to be brightly coloured.
True.
Petals of insect-pollinated flowers tend to be brightly coloured to attract pollinator insects.
What is the role of the anthers in flowers?
Anthers produce and release pollen.
What are the structures labelled X and Y in the diagram?
X and Y are:
X = anther
Y = stigma
True or False?
The pollen grains of insect pollinated flowers are smaller and lighter than those produced by wind pollinated flowers.
False.
Insect pollinated flowers produce large, sticky pollen grains, while wind pollinated flowers produce small, light pollen grains.
Define the term pollination.
Pollination is the process of transferring pollen from the anther to the stigma of a flower.
Describe fertilisation in plants.
Fertilisation in plants involves the fusion of a pollen nucleus with an ovule nucleus.
How are the stigmas of insect pollinated flowers adapted for pollination?
The stigmas of insect pollinated flowers are sticky in order to collect pollen grains from the bodies of visiting insects.
How are anthers adapted in wind-pollinated plants?
Anthers are adapted in wind-pollinated plants by swinging on long filaments outside the flower to allow the wind to catch pollen grains.
True or False?
Seed germination requires water, oxygen and cold temperatures.
False.
Seed germination requires water, oxygen and warmth. This is because the temperature needs to be suitable for enzyme activity.
What is self-pollination? (Extended Tier Only)
Self-pollination occurs when pollen is transferred from the anther of a flower to:
the stigma of the same flower
the stigma of another flower on the same plant
What is cross-pollination? (Extended Tier Only)
Cross-pollination occurs when pollen is transferred from the anther of a flower to the stigma of a flower from another plant of the same species.
True or False?
Self-pollination reduces the ability of a plant population to respond to changes in the environment. (Extended Tier Only)
True.
Self-pollination results in the production of offspring that are less genetically diverse (although they are not clones), meaning that they have a reduced ability to respond to changes in their environment.
Describe how fertilisation occurs in plants. (Extended Tier Only)
Fertilisation in plants involves the following:
a pollen tube grows down the style towards the ovary
pollen nuclei travel down the pollen tube to the ovary
a pollen nucleus fuses with an ovule nucleus in the ovary
What are the structures labelled A-D in the diagram?
The structures are:
A = urethra
B = penis
C = sperm duct
D = testes/testis
What are the structures labelled A-D in the diagram?
The structures are:
A = oviduct
B = ovary
C = cervix
D = vagina
What is the function of the testes in the male reproductive system?
The testes are responsible for the production of sperm cells. They also secrete the hormone testosterone, essential for the development of male reproductive organs and secondary sexual characteristics.
True or False?
The prostate gland secretes a fluid that nourishes and protects sperm.
True.
The prostate gland produces a fluid that contributes to semen volume. This fluid contains enzymes and nutrients that support sperm motility, as well as substances that help neutralise the acidity of the female reproductive tract.
What is the role of the cervix in the female reproductive system?
The cervix is a ring of muscle between the vagina and the uterus. It keeps the developing fetus inside the uterus during pregnancy and dilates during birth to allow passage of the baby through the vagina.
What is the role of the uterus in the female reproductive system?
The uterus is where the developing embryo implants and develops during pregnancy.
What is fertilisation in the context of human reproduction?
Fertilisation in human reproduction is the fusion of the nuclei of an egg and sperm cell.
What are the adaptive features of sperm cells?
The adaptive features of sperm cells include:
flagellum for swimming
many mitochondria to release energy for swimming
enzymes in the acrosome for entry into the egg cell
What are the adaptive features of egg cells?
Adaptive features of egg cells include:
energy stores within the cytoplasm
the jelly coat that changes at fertilisation to allow entry of a single sperm cell
True or False?
Egg cells are larger, fewer in number and more motile than sperm cells.
False.
Egg cells are larger and fewer in number than sperm cells, but they are not motile, meaning that they do not move around by themselves.
Define the term embryo.
The embryo is a ball of cells that develops from the zygote.
What are the structures labelled A-D in the diagram?
The structures are:
A = placenta
B = amniotic sac
C = umbilical cord
D = amniotic fluid
What is the function of the placenta? (Extended Tier Only)
The function of the placenta is to allow exchange of substances between the mother's blood and that of the fetus. Exchanged substances include:
dissolved nutrients
gases
excretory products
True or False?
Pathogens cannot cross the placenta while some toxins can. (Extended Tier Only)
False.
Both pathogens and toxins can cross the placenta.
What are secondary sexual characteristics?
Secondary sexual characteristics are features that are not present at birth but that develop during puberty.
What are the two hormones that control the development of secondary sexual characteristics?
The two hormones that control the development of secondary sexual characteristics are:
oestrogen in females
testosterone in males
Give examples of secondary sexual characteristics that develop in females.
Examples of secondary sexual characteristics that develop in females include:
breast development
growth of body hair
widening of hips
menstruation
growth of sex organs
Give examples of secondary sexual characteristics that develop in males.
Examples of secondary sexual characteristics that develop in males include:
growth of sex organs
growth of facial and body hair
voice breaking
sperm production
What is the menstrual cycle?
The menstrual cycle is the sequence of events that includes the thickening of the uterus lining, ovulation and menstruation; it is controlled by a series of hormones.
Define the term ovulation.
Ovulation is the release of an egg cell from the ovaries during the menstrual cycle.
From where are oestrogen and progesterone secreted during the menstrual cycle? (Extended Tier Only)
Oestrogen and progesterone are secreted from the ovaries.
Specifically, oestrogen is secreted by the developing follicle and progesterone by the empty follicle, known as the corpus luteum.
What is the role of FSH in the menstrual cycle? (Extended Tier Only)
FSH causes an egg to start maturing in the ovary. It also stimulates the ovaries to start releasing oestrogen.
True or False?
LH causes egg cells to start to mature within the ovaries. (Extended Tier Only)
False.
LH causes ovulation to occur.
It is FSH that causes an egg cell to begin to mature.
What is the role of oestrogen in the menstrual cycle? (Extended Tier Only)
Oestrogen causes the uterus lining to thicken during the first part of the menstrual cycle. It also interacts with other hormones to bring about maturation of an egg cell.
True or False?
An increase in progesterone results in the loss of the uterus lining. (Extended Tier Only)
False.
A decrease in progesterone levels at the end of the cycle results in the loss of the lining during menstruation.
Define the phrase sexually transmitted infection.
A sexually transmitted infection is an infection that is transmitted through sexual contact.
What is HIV?
HIV is a pathogen that causes an STI. HIV stands for human immunodeficiency virus.
True or False?
HIV is the same as AIDS.
False.
HIV is a pathogen and infection with HIV can lead to the disease AIDS.
How is HIV transmitted?
HIV is transmitted via body fluids, e.g. during sexual intercourse, contaminated blood, sharing needles, or across the placenta.
How can the spread of STIs be controlled?
The spread of STIs can be controlled by:
the use of condoms
testing for the presence of HIV so that infected individuals do not pass on the infection without knowing
education