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OCR GATEWAY GCSE BIOLOGY > B1 Cell level systems > Flashcards

B1 Cell level systems Flashcards

1
Q

What is a eukaryotic cell?

A

-Type of cell found in plants and animals.
-Contains a nucleus and membrane-bound organelles.

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2
Q

What is the nucleus?

A

-Contains the genetic material arranged as chromosomes.
-Controls the cell’s activities.
-Contains instructions to make new cells.

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3
Q

What is the cytoplasm?

A

A jelly-like substance that fills the cell and is the site of chemical reactions.

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4
Q

What are the ribosomes?

A

Site of protein synthesis.

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5
Q

What are the mitochondria?

A

Site of aerobic respiration.

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6
Q

What is the cell membrane?

A

-A selective barrier which controls which substances enter / leave the cell.
-Contains receptor molecules to help identify the cell.

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7
Q

What is the cell wall in a eukaryotic cell?

A

-Made of tough cellulose.
-Surrounds and supports the cell.

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8
Q

What is the sap vacuole?

A

Contains cell sap (a water solution of sugars and salts) which helps to support the plant.

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9
Q

What are chloroplasts?

A

-Contain green pigment, chlorophyll.
-Used in photosynthesis to transfer light energy from the sun / environment.

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10
Q

What does an animal cell contain?

A

-Nucleus.
-Cytoplasm.
-Cell membrane.
-Mitochondria.
-Cytoplasm.

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11
Q

What does a plant cell contain?

A

-Cytoplasm.
-Cell membrane.
-Cell wall.
-Mitochondria.
-Sap vacuole.
-Nucleus.
-Chloroplasts.

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12
Q

What is a prokaryotic cell?

A

A unicellular type of cell like bacteria which is very small to allow it to reproduce quickly and effectively.

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13
Q

What does a bacterial cell contain?

A

-Slime capsule.
-Pili.
-Cell wall.
-Cell membrane.
-Genetic material.
-Ribosomes.
-Cytoplasm.
-Plasmids.
-Flagella.

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14
Q

How does a bacterial cell store genetic material?

A

As long, circular strands of DNA that float freely in the cytoplasm.

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15
Q

What are plasmids?

A

Circular chromosomes (rings of DNA).

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16
Q

What are the flagella?

A

Allow prokaryotic cells to move through liquids.

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17
Q

What are pili?

A

Allow the cell to attach to structures.

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18
Q

What is the slime capsule?

A

Protects the cell.

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19
Q

What is the purpose of cell wall in a prokaryotic cells?

A

-Made of peptidoglycan.
-Holds the cell together.

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20
Q

What are features of a eukaryotic cell?

A

-Has a nucleus.
-DNA located in nucleus.
-Has membrane-bound organelles.
-DNA is held in linear chromosomes.
-Cell wall isn’t always present.
-Cell wall is made of cellulose.
-Can be unicellular / multicellular.
-Has no flagella.
-Large and complex cells (10-100 micrometers).

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21
Q

What are features of a prokaryotic cell?

A

-Has no nucleus.
-DNA contained within the cytoplasm.
-Has no membrane-bound organelles.
-DNA is held in plasmids.
-The cell wall is always present.
-Cell wall is made of peptidoglycan.
-Only unicellular organisms.
-May have flagella for movement.
-Small and simple cells (0.2 to 2 micrometers).

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22
Q

What is the equation for total magnification?

A

Total magnification = magnification of eyepiece lens x magnification of objective lens

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23
Q

Why do scientists use staining?

A

Most cells are colourless so staining allows different parts of a cell to be seen more clearly.

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24
Q

How does methylene blue stain work?

A

Stains the nucleus of an animal cell.

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25
Q

How does iodine stain work?

A

Stains the nucleus of a plant cell.

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26
Q

How does crystal violet stain work?

A

Stains bacterial cell walls.

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27
Q

What is the definition of magnification?

A

How many times larger the image appears compared to the object.

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28
Q

What is the definition of resolution?

A

The ability to distinguish between two points that are close to each other.

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29
Q

What is an image?

A

What you see under the microscope.

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30
Q

What is an object?

A

What you’re examining under the microscope.

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31
Q

What is the formula for magnification?

A

Magnification = image size / object size.

Image size and object size must be in same units.

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32
Q

What are advantages of light microscopes?

A

-Relatively cheap.
-Portable.
-Doesn’t require specialist training.
-Can look at living specimens.

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33
Q

What are disadvantages of light microscopes?

A

-Low resolution (200nm) as limited by the wavelength of visible light.
-Low magnification strength (x1500).
-Staining required to see some organelles.

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34
Q

What is an electron microscope and why is it more effective than a light microscope?

A

-Uses electrons instead of light to form images.
-More effective than light microscopes as electrons have a much smaller wavelength than light waves therefore scientists can view smaller, sub cellular structures like mitochondria and ribosomes.

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35
Q

What are the 2 types of electron microscope?

A

-SEM (Scanning Electron Microsocope).
-TEM (Transmission Electron Microscope).

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36
Q

What is an SEM?

A

-Large depth of field so can examine the surface structure of specimens.
-Creates 3D images at lower resolution of 10nm.
-Tend to be used at lower magnifications of x100,000.

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37
Q

What is depth of field?

A

The distance between nearest and furthest objects in focus.

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38
Q

What is a TEM?

A

-Creates 2D images detailing organelles at a higher resolution than SEM (0.2nm).
-Maximum magnification of x1,000,000 but images can be enlarged beyond that photographically.

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39
Q

What are advantages of electron microscopes?

A

-Can see very small organelles.
-Can produce 3D images (SEM).
-Can see images at very high resolution.

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40
Q

What are disadvantages of electron microscopes?

A

-Cannot look at living specimens as samples need to be placed in a special vacuum.
-Extremely expensive.
-Very large so cannot be moved easily.
-Requires specialist training and skill.

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41
Q

What is DNA?

A

-Deoxyribonucleic acid.
-A chemical that holds all the genetic information of an organism and therefore controls growth and development.
-Carries a set of instructions that make all the proteins required for life.
-Made up of a chain of nucleotides that form chromosomes.
-Made from 4 different nucleotides.

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42
Q

Why is DNA a polymer?

A

DNA is a polymer made from 2 strands of nucleotides (monomers) that are coiled together in a double helix shape (double stranded spiral).

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43
Q

What is a chromosome?

A

-A long strand of coiled up DNA.
-Divide into smaller sections, genes.

44
Q

What is a gene?

A

A short section of DNA that codes for specific sequences of amino acids, creating specific proteins and controlling characteristics.

45
Q

What does a nucleotide consist of?

A

-1 deoxyribose sugar.
-1 phosphate group (that forms the sugar phosphate backbone).
-1 of the 4 different organic bases.

46
Q

What are the 4 different nucleotides that make up DNA?

A

-Cytosine.
-Guanine.
-Adenine.
-Thymine.

47
Q

What is complimentary base pairing?

A

-Only certain bases join together so the bases of one DNA strand form strong cross-links with complementary bases on the other strand.
-Cytosine + Guanine.
-Adenine + Thymine.

48
Q

Why does a change to the DNA base sequence impact the protein produced?

A

Order of bases in DNA dictates which amino acids will be used to build the protein as each triplet code codes for a specific amino acid.

49
Q

What is a DNA sequence?

A

Collection of groups which consists of 3 bases.

50
Q

What is a triplet code?

A

Group of 3 bases which contains all the information to code for a single specific amino acid.

51
Q

What’s the difference between DNA and mRNA?

A

-DNA is double stranded whereas mRNA is single stranded.
-DNA pairs Adenine and Thymine whereas mRNA pairs Adenine and Uracil.
-DNA has deoxyribose sugar whereas mRNA has ribose sugar.

52
Q

Why are proteins polymers?

A

They are polymers made up of chains of monomers, amino acids.

53
Q

Why are there different types of proteins with different functions?

A
  1. The amount, type and order of amino acids in the chain is variable.
  2. This results in many types of proteins that differ in shape.
  3. The shape of the protein helps to define its function.
54
Q

What is a protein?

A

A large molecule synthesised from amino acid monomers.

55
Q

What is protein synthesis?

A

The formation of proteins from amino acids which takes place in the ribosomes.

56
Q

What are the 2 stages of protein synthesis?

A

-Transcription: occurs in the nucleus and is the unzipping of the DNA molecule around the gene, copying it to mRNA in the nucleus.
-Translation: occurs in cytoplasm where the mRNA attaches to the ribosome and translates the mRNA sequence into an amino acid sequence by recruiting tRNAS carrying amino acids in order to make a polypeptide chain and form a protein.

57
Q

What is the process of protein synthesis?

A

Transcription:
1. DNA double helix structure is untwisted and unzipped to expose one strand of DNA.
2. mRNA nucleotides match to their complementary bases on the exposed strand.
3. the DNA double helix structure zips back up and the mRNA nucleotides are joined together, creating a new strand called the template strand of the original DNA.

Translation:
4. The mRNA template strand moves out of the nucleus and attached itself to a ribosome in the cytoplasm, recruiting tRNA molecules that have complementary anti-codons to the codons in the mRNA sequence.
5. The ribosome reads the bases on the mRNA template strand in triplet codes and for each codon, the tRNA molecule with the complementary anti-codon brings a specific amino acid.
6. Each amino acid joins together to form a polypeptide chain and once the chain is complete, the polypeptide chain folds into a unique 3D structure and forms a protein.

58
Q

What are enzymes?

A

-Act as biological catalysts to speed up the rate of a chemical reaction without being used up or changed in the reaction.
-Reduce the need for high temperature.
-Necessary to all living organisms as they allow all metabolic reactions to occur at a rate that can sustain life.

59
Q

What is a substrate?

A

The molecule being changed in a reaction.

60
Q

What is an active site?

A

A specifically shaped region in an enzyme which allows it to bind to the substrate.

61
Q

How does an enzyme work in the lock and key hypothesis?

A
  1. When the enzyme and substrate molecules meet, they react together at the active site to form an enzyme-substrate complex.
  2. The enzyme substrate complex breaks down into the enzyme and products.
  3. The products are released from the active site and now the enzyme can be used again.
62
Q

Why do different biological reactions all have a specific enzyme to help control the reaction?

A

-The lock and key hypothesis indicates that the substrate and enzyme must be complementary to each other in order for the reaction to be catalysed.
-This proves that each type of enzyme is specific to one type of reaction.

63
Q

What is the effect of temperature on the rate of an enzyme-controlled reaction?

A

-As the temperature increases, the rate of an enzyme-controlled reaction also increases until increased beyond the optimum temperature.
-Enzymes work fastest at their optimum temperature, 37 degrees celsius.
-Increasing temperature causes enzyme and substrate molecules to have more kinetic energy, move faster, and collide more frequently.

64
Q

Why does the rate of an enzyme-controlled reaction decrease beyond the optimum temperature?

A

-Enzymes begin to denature as these high temperatures will break the bonds holding the enzyme together and the active site will lose its shape so the substrate can no longer fit and the enzyme can no longer catalyse the reaction so it stops.
-The denaturing is permanent.

65
Q

What is the effect of pH on the rate of an enzyme-controlled reaction?

A

-As the pH increases, the rate of an enzyme-controlled reaction also increases until beyond the optimum pH.
-Enzymes work fastest at the optimum pH, 7, in humans.
-Enzymes in acidic conditions have low optimum pH whereas in alkaline conditions, high optimum pH.

66
Q

Why will the rate of enzyme-controlled reaction stop increasing beyond the optimum pH?

A

-Enzymes will denature as the hydrogen bonds holding the amino acid chain together to make up the protein can be disrupted/broken.
-This changes the shape of the active site so the substrate can no longer fit into it and the enzyme can’t catalyse the reaction.

67
Q

What is the effect of enzyme / substrate concentration on the rate of an enzyme-controlled reaction?

A

-As the enzyme / substrate concentration increases, the rate of an enzyme-controlled reaction also initially increases.
-Stops increasing when all the substrates are used up so nothing for extra enzymes to react with / all available active sites become satires so nothing for extra substrates to react with as enzyme and substrate need to react to form enzyme-substrate complex.

68
Q

What is cellular respiration?

A

A universal chemical process which occurs continuously in all living cells to supply them with energy in the form of ATP from the breakdown of organic compounds like glucose.

69
Q

Why is cellular respiration an exothermic reaction?

A

It releases energy.

70
Q

What are the 2 types of cellular respiration?

A

-Aerobic respiration.
-Anaerobic respiration.

71
Q

What is energy, in the form of ATP, required for?

A

-Chemical reactions to build up large molecules from smaller ones (proteins from amino acids or starch and cellulose from glucose).
-Muscle contraction to allow movement.
-Keeping warm to maintain a constant temperature suitable for enzyme activity.
-Supplies energy needed for metabolic processes to occur within cells and organisms generally.

72
Q

What is metabolism?

A

All the chemical reaction in the cells of an organism.

73
Q

What is aerobic respiration?

A

Requires oxygen and is the chemical reaction in cells that uses oxygen to completely breakdown glucose to release a large amount, 38 ATP per molecule of glucose, of energy.

74
Q

What is anaerobic respiration?

A

Doesn’t require oxygen and is the chemical reaction in cells that incompletely breaks down glucose to release some, 2 ATP for every molecule of glucose, energy.

75
Q

What is the equation for aerobic respiration?

A

-Glucose + oxygen -> carbon dioxide + water.

-C6H12O6 + 6O2 -> 6CO2 + 6H2O.

76
Q

Why does anaerobic respiration have different breakdown products?

A

Process is different for different organisms (animals or plants and fungi) so different breakdown products are formed depending.

77
Q

What is the equation for anaerobic respiration in humans / animals?

A

-Glucose -> lactic acid.

-C6H12O6 -> 2C3H6O3.

78
Q

What is the equation for anaerobic respiration in plants / fungi?

A

-Glucose -> Ethanol + Carbon Dioxide.

-C6H12O6 -> 2C2H6O + 2CO2.

79
Q

What is the process of anaerobic respiration in humans / animals?

A
  1. Mainly takes place in the muscle cells during vigorous exercise.
  2. Muscles have higher demands for energy when individuals exercise at high intensities.
  3. Bodies can only deliver so much oxygen to muscle cells for aerobic respiration.
  4. When oxygen becomes a limiting factor, glucose is broken down without it, producing lactic acid and some energy as glucose isn’t fully broken down.
  5. Lactic acid buildings up in the muscle cells and lowers the pH of the muscle tissue, making conditions more acidic which can potentially denature the enzymes in the cells.
  6. If lactic acid builds up in blood and muscles, they feel tired and ache and cause oxygen debt.
  7. After vigorous exercise, the heart continues to pump fast to transport the lactic acid in the blood from the muscles to the liver to be broken down.
  8. Breathing also remains deep to supply extra oxygen (oxygen debt) needed to oxidise lactic acid into carbon dioxide and water through aerobic respiration.
80
Q

What is oxygen debt?

A

The amount of oxygen required to break down the lactic acid that has built up.

81
Q

What is repaying the oxygen debt?

A

Process of breaking down the lactic acid.

82
Q

What is the process of anaerobic respiration in plants / fungi?

A

Fermentation: anaerobic respiration in yeast and is important in the manufacture of bread where CO2 produced helps the dough to rise, and in brewing (beer made from ethanol).

83
Q

What are carbohydrates?

A

-Polymers made up of monomers, simple sugars.
-Contain the elements carbon, oxygen and hydrogen.
-Broken down by carbohydrase enzymes, like amylase, in the mouth and small intestine.

84
Q

What is an example of breakdown for carbohydrates?

A

Amylase enzyme breaks down starch into maltose, a simple sugar that can go into the blood to provide energy.

85
Q

What is an example of synthesis for carbohydrates?

A

Glycogen synthase enzyme releases glucose as glycogen, an energy store.

86
Q

What are proteins?

A

-Polymers formed from long chains of monomers, amino acids, joined together.
-Contain the elements carbon, oxygen, hydrogen and nitrogen.
-Broken into amino acids by protease enzymes in the stomach and small intestine.

87
Q

What is an example of synthesis in proteins?

A

20 different types of amino acids make up all proteins depending on their different arrangements.

88
Q

Why does every protein have a unique 3D shape to carry out its function?

A

A protein’s function is determined by its shape and different proteins have different amino acid sequences, resulting in the peptide chain folding into different shapes.

89
Q

What are lipids?

A

-Fats when they are solid at RTP.
-Oils when they are liquid at RTP.
-Contain elements carbon, oxygen and hydrogen.
-Broken down by a lipase enzymes in the small intestine.

90
Q

What makes up a lipid?

A

One glycerol molecule chemically bonded to 3 fatty acid chains.

91
Q

Is a lipid a polymer?

A

No as they don’t form a long chain of repeating sub-units.

92
Q

Where is bile made?

A

In the liver.

93
Q

Why does bile emulsify fat?

A

This makes large fat molecules into small droplets so it’s easier for lipase enzymes to work on lipids.

94
Q

What is photosynthesis?

A

An endothermic reaction in which light energy from the environment is absorbed by the chlorophyll, green pigment, in chloroplasts to make glucose.

95
Q

What are photosynthetic organisms?

A

Main producers of food and therefore biomass for life on earth.

96
Q

What is the equation for photosynthesis?

A

-Carbon dioxide + water -> glucose + oxygen.

-6CO2 + 6H2O -> C6H12O6 + 6O2.

97
Q

In photosynthesis, where do reactants come from and where do products go?

A

-Carbon dioxide diffuses into the lead through the stomata.
-Water is absorbed by the roots and transported to the leaves through the xylem.
-Glucose is used to make substances the plant needs and energy for respiration.
-Oxygen diffuses out the leaf through the stomata and is used in respiration.

98
Q

What is chlorophyll?

A

-Helps chloroplasts absorb as much light energy as possible.
-Most plants have leaves that contain mesophyll cells which are packed with chloroplasts to maximise the amount of photosynthesis.

99
Q

What are the 2 stages of photosynthesis?

A
  1. Light-dependent stage: light energy is absorbed by the chlorophyll in chloroplasts to split water into oxygen gas and hydrogen ions.
  2. Light independent stage: carbon dioxide gas taken from the atmosphere then combines with the hydrogen ions to make glucose.
100
Q

What are uses of glucose in plants?

A

-Used to produce energy in respiration.
-Lots of glucose molecules join together to form cellulose, providing cell walls with strength.
-Can combine with nitrate ions, absorbed by soil, to produce amino acids for photosynthesis.
-Can be stored as insoluble starch in leaves, stems and roots of plants so plant will have glucose available in times it can’t photosynthesise.
-Can be stored in seeds as fats and oils.

101
Q

How does temperature affect the rate of photosynthesis?

A

-As the temperature increases, so does the rate of photosynthesis until the temperature is increased beyond the optimum temperature.
-The temperature affects the speed at which carbon dioxide move through a plant.
-When increased, the kinetic energy of particles also increases and this increases the frequency of collisions between particles, resulting in a higher formation of products.

102
Q

Why does the rate of photosynthesis decrease beyond the optimum temperature?

A

Enzymes that control the process of photosynthesis will start to denature, reducing the overall rate of photosynthesis.

103
Q

What is the effect of light intensity on the rate of photosynthesis?

A

-As light intensity increases, so does the rate of photosynthesis as this provides the photosynthetic organism with more light energy so the reaction occurs faster.
-Will continue to increase rate until the rate is limited by another factor required for photosynthesis being in short supply.

104
Q

What is the effect of carbon dioxide on the rate of photosynthesis?

A

-As the carbon dioxide concentration increases, so does the rate of photosynthesis as providing the photosynthetic organism with more carbon dioxide speeds up the reaction.
-Will continue to increase the rate until the rate is limited by another factor required for photosynthesis being in short supply.

105
Q

How can the amount of chlorophyll limit the rate of photosynthesis?

A

-Less chlorophyll results in less light energy being absorbed and therefore reduces the rate of photosynthesis.
-Disease / environmental stress (like lack of mineral ions) can affect the amount of chlorophyll present in a plant.

106
Q

Can more than one limiting factor impact the rate of photosynthesis?

A

-More than one limiting factor can impact rate of photosynthesis.
-Initially, it will be one factor but once the graph levels off, another factor becomes the limiting factor.
-Can compare experiments in a graph / the curve in a graph to figure out the limiting factor.

107
Q

What is the inverse square law?

A

-Shows the relationship between light intensity and distance as inversely proportional.

Light intensity (lux) = 1 / distance squared

OCR GATEWAY GCSE BIOLOGY (6 decks)

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