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# Science Revision for Mid-Year Exam

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## Deanne Hornigold

on 2 November 2013

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#### Transcript of Science Revision for Mid-Year Exam

Genetics and Inheritance
Science Targets for mid-term Exam
Plants and Photosynthesis
Metals
1. Describe the difference in chromosome numbers in gametic and somatic cells
A Gametic cell (or sex cell) contains half the standard amount of 46 (So 23) chromosomes whilst a Somatic cell has a full set.
2. Predict the likely genotypes and phenotypes of the following crosses using punnet squares:
This punnet square displays two Heterozygous and the phenotypes that they can produce.
Ratio: 3:1
Probabilities: 75%, 25%, 0.75, 0.25
Ratio: 1:0

Probabilities: 100%, 0%, 1, 0
This punnet square shows a Homozygous dominant and a Homozygous recessive and

phenotypes they can produce.

Ratio: 1:0

Probabilities: 100%, 0%, 1, 0
This punnet square shows a Homozygous dominant and a Heterozygous and the phenotypes

that they can produce.

This punnet square displays a Homozygous recessive and a Heterozygous and the phenotypes they can produce.

Ratio: 1:1

Probabilities: 50%, 50%, 0.5, 0.5
3. Explain why the predicted phenotypes of offspring do not necessarily match the actual phenotypes.
Because the combination of DNA and alleles is all chance and each child will have the same

chance as the one before it, (once an option is taken it does not become unavailable)

however the more offspring that you have the more you will curve to the trend and follow

the statistic pattern, (someone actually having enough offspring to do so however is near

impossible).
4. Deﬁne these terms.
Chromosome: Many DNA molecules joined together forming many genes strung together, inherited from parents through sex cells.
Allele: A gene variable, determines characteristics
Dominant: An allele that will always show up if present.
Recessive: An allele that will only show up if no dominant genes are present
Homozygous: Two of the same alleles, eg. AA or aa.
Heterozygous: Different alleles, eg. Aa.
Genotype: Genetic makeup, details of alleles.
Phenotype: How it appears, eg. lets say straight hair is dominant than the allele for someone with curly hair would be aa and the phenotype would be curly hair. (So the visible trait is the phenotype, traits that involve cutting someone open to see count as well).
Selective Breeding: Selective breeding is a process in which you breed animals or plants together in a particular way either to discover or preserve a valuable trait/phenotype.
Cloning: Making an exact genetic replication of a living organism
5. Compare and contrast selective breeding and cloning.
Half of the double helix 'spine' or strand consists of phosphate molecules whilst the other half is formed of sugar, this together produces the 'Sugar Phosphate Backbone'. In between both sides of the double helix are nitrogenous bases these are linked together by weak hydrogen bonds, these bases consist of four different types; Adenine, Thymine, Guanine and Cytosine. These bases pair with each other, Adenine with Thymine and Guanine with Cytosine. If the bases pair with the wrong opposite base (eg. Adenine and Cytosine) there will be a mutation.
6.Explain the structure of a DNA molecule.
7. Describe how mutations occurs.
Mutations occur when nucleic bases pair off with the wrong partner, this can occur when the DNA sequence is developing in the womb. Mutations can also occur as the sun's ultra violet rays break the weak hydrogen bonds holding the bases together, the bases will try to re-partner but if they pair off wrong there will be a mutation caused.
8. Explain the effects of genetic mutations.
Genetic mutations can have many different effects they are generally disadvantageous such as Cystic Fibrosis, which causes the lungs to be constantly filled with a heavy, thick, sticky form of mucus. Yet some mutations can be advantageous for example bacteria are constantly changing and becoming immune to antibiotics as they live in such vast populations that some of them are sure to have a mutation which will allow them to survive the antibiotic used against them, consequently as they are the only ones left in the area treated with antibiotics they are the only ones left capable of passing on genes and so a whole population of antibiotic immune bacteria has been created. Some mutations are 'Silent' however and have no negative or positive effect on the organism, (blue eyes for example).
9.Identify the products and reactants in photosynthesis.
The products reactants are as follows;
Reactants: Carbon Dioxide, Water, Light, Chlorophyll.
Products: Oxygen and Glucose.
Sun's Energy
Co2 + H2O --------------------|> O2 + C6H1206
Chlorophyll
Excellence= Chemical Formula for Photosynthesis
Merit= Word equation for Photosynthesis
Light
Carbon dioxide + Water --------------------|> Oxygen + Glucose
Chlorophyll
10. Explain the difference and roles of chloroplasts and chlorophyll.
Chloroplast: is a plant cell in which photosynthesis occurs. Chloroplasts contains Chlorophyll and filters sun light into the Chlorophyll.
Chlorophyll: green pigment that absorbs and stores sun light.
11. Describe factors that affect the rate of photosynthesis.
The things that affect the growth of a plant are called 'limiting factors,' This includes:
Light intensity
Temperature
Carbon dioxide
The higher the temperature then typically the greater the rate of photosynthesis, photosynthesis is a chemical reaction and the rate of most chemical reactions increases with temperature. However, for photosynthesis at temperatures above 40°C the rate slows down. This is because the enzymes involved in the chemical reactions of photosynthesis are temperature sensitive and destroyed at higher temperatures.
Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. During the night the sun does not give off any energy, therefore no photosynthesis occurs. Increasing the light intensity will boost the speed of photosynthesis. Though, too much light at a high intensity can damage chloroplasts.
Bibliography

http://www.passmyexams.co.uk/GCSE/biology/factors-affecting-rate-of-photosynthesis.html
http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/environment/1_food_factory2.shtml
http://www.scribd.com/doc/6946792/Factors-affecting-the-rate-of-photosynthesis
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/chemicalreactions/preparinggasesrev4.shtml
Plants take in carbon dioxide from the atmosphere and use it to produce oxygen. However, an abundance of carbon dioxide does not necessarily increase the rate of photosynthesis. The enzymes that join organic molecules with carbon atoms absorb the carbon dioxide until they reach a point of saturation and are incapable of absorbing any more. This means that there is a limit to how much carbon dioxide a plant can absorb and use, so the rate of photosynthesis levels off after reaching this point rather than absorbing endless amounts of the gas.

12. Explain when and where starch is produced in a plant.
Starch is produced in the leaves of plants during the night when no photosynthesis can occur, it is then transferred down the xylem to the roots for storage. Starch is produced by the chloroplasts when too much glucose is being made. Lots of glucose will be made when the plant is photosynthesizing a lot e.g. on a warm and sunny day.
13. Describe how to test whether starch is present in a plant.
What's the test for starch?
Use a substance called iodine.
If starch is present, iodine will turn blue/black.
If there is no starch, then iodine will stay its brown colour.
Brown colour=no glucose=no photosynthesis (as it has not received any light)

14. Explain how to de-starch a plant.
Leave the plant in the dark for 48 hours. It will not be able to photosynthesize without light, so it will use up all its stored starch to make energy.
15. Label the parts of a leaf and explain the role of each part.
Diagram of a leaf
Role of each part
16. Discuss the process and role of transpiration in plants including the structures that are involved.
Transpiration is the process by which plants lose water.
It normally happens from the leaves of plants – either when the stomata are open or from the surface of the cells in contact with the air.
Transpiration is useful to the plant to move water and minerals from the roots up the xylem to the leaves. It also helps to cool the plant down. However too much transpiration and the plant will lose water and become wilted.
What environmental conditions can increase the rate of transpiration?
Light, Temperature, Wind and Humidity
17. Explain the role of the rainforest in managing the role of carbon dioxide in the environment.
Rainforests are an important resource in managing CO2 levels in the atmosphere. If they are cut down there are fewer trees to absorb the CO2 and therefore levels will rise.
Plants use carbon dioxide for photosynthesis. Carbon dioxide from the atmosphere is converted into glucose and oxygen.
Too much CO2 in the atmosphere can lead to global warming, which causes climate change, rising sea levels and melting of ice caps.
Key Words:
Chromosomes, gamete, genotype, gene, sex chromosome, dominant, recessive, homozygous, hetrozygous, phenotype, mutation,selective breeding, cloning, sexual reproduction, asexual reproduction, offspring, allel, inherited variation, environmental variation, DNA
Key Words for Plants and Photosynthesis
Photosynthesis, carbon dioxide, water, light, chlorophyll, glucose, oxygen, light intensity, rate of photosynthesis, starch, variegated leaf, stomata, palisade mesophyll cells, waxy cuticle, spongy mesophyll, phloem, xylem, guard cell, transpiration, global warming, atmosphere.
Key Words for Metals
State, conductivity/conductors, malleability, magnetism, hydrogen, compound, carbon dioxide, neutralization, reactants, melting point.
19/20. Describe the differences between metals and non-metals

Non Metals: Non-Metals can be of any state at room temperature (solid, liquid or gas), Non-Metals if solid are often brittle, Non-Metals often have low melting points, Non Metals are dull or colourless and NONE are magnetic.
20/21. Explain how to test for carbon dioxide and hydrogen
Metals: Metals tend to be solids, the only exception being Mercury (Hg), Metals tend to have high melting points, the only exception being Mercury (Hg), Metals can be magnetic (the following are), Cobalt (Co), Iron (Fe), Tin (Sn) and Nickel (Ni), Metals are shiny, (if they aren't just scrape off the dull layer to see a shiny layer underneath), Metals are often good conductors, Metals are malleable (when heated to a certain point they can be shaped), Metals are sonorous (when in their solid form if struck they produce a ringing sound) and Metals can be ductile (can be stretched into wires), Metals are often grey or silver in colour, however Gold (Au) and Copper (Cu) do not follow this rule.
& Explain the physical properties of common metals and non metals.
We know a reaction occurs because, change is not returnable and a new substance is made.
Eg neutralisation is the reaction between an acid and alkali making a new salt and water [neutralisation]
Eg lime water goes cloudy when carbon dioxide is bubbled through [precipitation]
Eg hydrogen burns with an explosion [combustion]
How do we test for hydrogen gas?
The pop test is carried out to test for the presence of hydrogen. When a glowing splint is places over a boiling tube releasing hydrogen gas e.g. such as when a metal is added to an acid, it will make a loud pop
How do we test for Carbon dioxide gas?
A lighted wooden splint goes out in a test tube of carbon dioxide but this happens with other gases, too. It is better to bubble the test gas through limewater - calcium hydroxide solution. Carbon dioxide turns limewater cloudy white.
22. Predict the compounds formed from the reaction of metals with acids and oxygen.
Examples;
Magnesium, + Oxygen = Magnesium Oxide.
Mg + O2 = MgO2
Chromium + Oxygen = Chromium Oxide.
Cr + O2 = CrO2
23. Predict the compounds formed from the reaction of carbonates with acids.
A Metal Carbonate consists of a Metal mixed with Carbon and can be a Bicarbonate containing two oxygen atoms or a Carbonate containing three oxygen atoms. When a Metal Carbonate reacts with an Acid a Salt, Carbon Dioxide and Water is produced.
Tip: A salt is the Metal's name placed in front of the acid's second half name.
Example;
Magnesium Carbonate + Hydrogen Nitrate = Magnesium Nitrate + Carbon Dioxide + Water.
MgCO3 + 2HNO3 = Mg(NO3)2 + CO2 + H2O
When a Metal reacts with Oxygen, only a Metal Oxide is produced,
Tip: Take metal's name and place 'oxide' on the end.
24. Predict the compounds formed from the reactions between acids and alkalis.
Acids consist of positively charged H+ ions whilst Alkalies or bases consist of negatively
charged OH- ions. when these react with each other NEUTRALIZATION occurs as the
negative and the positive balance each other out and the Hydrogen and Oxygen elements
react together to form water, with Ph of 7 which is perfectly neutral.
Example;
Acid + Alkali = Water + Salt.
H+ + OH- = H2O + Varies
Primary Sources:
Secondary Sources:
Mr Cluett
Connor Wallace
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