Biology Topic 7

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Are human body cells haploid or diploid?
They are diploid. This means they have two copies of each chromosome, arranged in pairs. A human cell nucleus contains 46 chromosomes in total, so the diploid number for a human is 46.
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What does the nucleus contain?
This contains your genetic material in the form of chromosomes.
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What is a gene?
A short section of DNA. They are chemical instructions.
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What is a chromosome?
Long lengths of DNA coiled up.
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How are genes chemical instructions?
DNA is a long list of instructions on how to put an organism together and make it work. Each separate gene in a DNA molecule codes for a particular protein. These are important because they control processes in the body and inherited characteristics.
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What are different versions of the same gene called?
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What does DNA consist of?
Two strands coiled together in the shape of a double helix. The two strands are held together by bases. There are four bases. DNA is a type of nucleic acid.
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What are the four bases and how are they paired?
Adenie (A), Cytosine (C), Guanine (G), Thymine (T). A-T and C-G. This is called complementary base-pairing.
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Define asexual reproduction.
This involves only one parent. The offspring have identical genes to the parent- so there's no variation between parent and offspring.
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Does asexual reproduction involve mitosis or meiosis?
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What is mitosis?
An ordinary cell can make a new cell by dividing into two. Both new cells are genetically identical to the original and contain exactly the same genetic information.
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What are the steps of mitosis?
A diploid cell divides by mitosis. Interphase, Prophase, Metaphase, Anaphase, Telephase, Cytokinesis.
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Define sexual reproduction.
The fusion of male and female gametes. Because there are two parents, the offspring contain a mixture of their parents' genes.
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How does sexual reproduction produce genetically different cells?
The male and female produce gametes. Gametes are haploid, each containing 23 chromosomes. At fertilisation the M. gamete fuses with the F. gamete to form a zygote, which has a full set of chromosomes. Cell division, embryo. Inherits from both parents
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Are gametes produced by mitosis or meiosis?
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What are the stages of meiosis?
Interphase, Prophase 1, Metaphase 1, Anaphase 1, Telophase 1 and Prophase 2, Metaphase 2, Anaphase 2, Telephase 2 - four daughter cells, each with a single set of chromosomes and genetically different.
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What is the male reproductive part of the flower?
Stamen. This consists of the anther and filament. The anther contains pollen grains which produce M. gametes. The filament is the stalk that supports the anther.
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What is the female reproductive part of the flower?
Carpel. This consists of the ovary, style and stigma. The stigma is the end bit that the pollen grains attach to. The style supports the stigma. The ovary contains the female gametes.
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Define pollination.
The transfer of pollen from an anther to a stigma, so that the male gametes can fertilise the female gametes in sexual reproduction.
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Define cross-pollination.
A type of sexual reproduction where pollen is transferred from the anther of one plant to the stigma of another. Plants that do this rely on things like insects or the wind to help them pollinate.
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How are plants adapted for insect pollination?
Brightly coloured petals to attract insects. Scented flowers and nectaries (glands that secrete nectar). Produce big, sticky pollen grains- stick to insects as they go from plant to plant. Stigma is sticky.
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How are plants adapted for wind pollination?
Small, dull petals on the flower- no need to attract insects. No nectaries/strong scents. A lot of pollen grains- small, light- easily carried. Long filaments that hang the anthers outside the flower. Large, feathery stigma- catch pollen, outside.
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How does fertilisation in a plant take place?
(Fusion of gametes). Pollen grain lands on the stigma, pollen tube grows out of the pollen grain, down through the style to ovary. Nucleus from M. gamete moves down the tube, joins with a F. gamete in ovary. Fertilised F. gamete forms a seed.
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Define fertilisation.
The two nuclei fuse together to make a zygote. This divides by mitosis to form an embryo.
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What conditions do seeds need to germinate?
Water- activates the enzymes that break fown the food reserves in the seed. Oxygen- for respiration, provides energy for growth. Temperature- for enzymes to work.
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How do germinating seeds get energy?
The developed seed contains an embryo and a store of food reserves wrapped in a hard seed coat. Germination- glucose for respiration from store. Once the plant has grown enough to produce green leaves it can get its own food energy- photosynthesis.
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How can plants reproduce asexually using natural methods? Give an example.
Strawberry plants- send out runners (fast-growing stems that grow sideways). Runners take root at various points and new plants grow- clones.
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How can plants be cloned artificially?
Take cuttings from good parent plants then plant them to produce clones. Cuttings each have a new bud, kept in moist conditions until they are ready to plant.
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What are clones?
Genetically identical copies.
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What are the human male gametes?
Sperm. Made in the testes. Sperm mix with a liquid to make *****, ejaculated from the penis into the ****** during sexual intercourse.
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How is the male gamete transported around the body?
Urethra- tube caries sperm trhough the penis during ***********. Erectile tissue- swells when filled with blood, erect. Testis- made. Glands- produce liquid added. Vas deferens- muscular tube that carries sperm towards urethra from testis.
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What are the human female gametes?
Ocum. Made in the ovaries. Produced every 28 days, passes into the Fallopian tube, meets sperm during sexual intercourse. Fertilised- ovum divides, cells travel down F. Tube to uterus, attach to the endometrium. Develops into embryo.
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How is the female gamete transported around the body?
Fallopian tube- muscular tube, ovum from ovary to uterus. Muscular uterus walls. Uterus- growth of embryo. Endometrium- good blood supply for implantation of embryo.
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What hormone promotes sexual characteristics at puberty in females?
Oestrogen. Extra hair on underarms+pubic area. Hips widen. Development of breasts. Ovum release and start of periods.
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What hormone promotes sexual characteristics at puberty in males?
Testosterone. Extra hair on face+body. Muscles develop. Penis and testicles enlarge. Sperm production. Deepening of voice.
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What are the four stages of the menstrual cycle?
1- day 1 is when the bleeding starts. 2- uterus lining builds up again, d4-14. 3- an ovum develops and is released, d14. 4-wall is maintained for 14days until d28, if no fertilisation, spongy lining breaks down. Start again.
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How do oestrogen and progesterone control the menstrual cycle?
Oestrogen- causes the lining of the uterus to thicken and grow, stimulates the release of an ovum at d14. Progesterone- maintains the lining of the uterus, level of this falls, lining breaks down.
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How does the embryo develop during pregnancy?
Embryo is implanted, placenta develops= blood of embryo and mum get close and allows the exchange of food, oxygen and waste. Amnion membrane forms, surrounds the embryo and is full of amniotic fluid, protects embryo against knocks and bumps.
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What is homozygous?
Two alleles that are the same for that particular gene, eg CC.
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What is hetrozygous?
Two different alleles for that particular gene, eg Cc.
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What is the genotype?
Alleles that you have.
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What is the phenotype?
Characteristics the alleles produce.
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What are codominant alleles?
Neither allele is recessive, show characteristics from both- eg blood group AB.
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What is a family pedigree?
A family tree of genetic disorders.
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How do your chromosomes control your gender?
Y chromosome causes male. 23 matched pairs of chromosomes in every human body cell, XY or XX determine your gender.
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What is genetic variation caused by?
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What are most variations in animals due to?
Genes and the environment. EG. Baby's weight at birth is affected by mothers diet. Eye colour is not environmental.
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What is the environmental variation in plants?
Sunlight, moisture level, temperature, mineral content of the soil.
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What is the theory of evolution?
Life began as simple organisms from which more complex organisms evolved.
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\What is natural selection?
Survival of the fittest. All living things show variation, resources are limited so animals need to compete for them.
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Why is it the best genes for a particular environment tend to survive?
Well suited to the area in which it lives, more likely to pass their alleles on.
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What is a mutation?
A change to the genetic code. Occasionally a gene may mutate by it is rare, however can be inherited. They change the sequence of the DNA bases. They happen spontaneously, but at more risk is if exposed to ionising radiation, or mutagens.
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Why are mutations harmful?
Occurs in reproductive cells, offspring might develop abnormally or die. Mutant cells might start to multiply in an uncontrolled way and invade other parts of the body (Cancer).
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How can bacteria evolve to be antiobiotic-resistant?
Bacteria can develop random mutations in their DNA, changing their characteristics- less affected by a particular antibiotic. Lives longer, reproduces more, becomes more immune.
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Card 2


What does the nucleus contain?


This contains your genetic material in the form of chromosomes.

Card 3


What is a gene?


Preview of the front of card 3

Card 4


What is a chromosome?


Preview of the front of card 4

Card 5


How are genes chemical instructions?


Preview of the front of card 5
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