Edexcel GCSE 9-1 Biology - SB1: Key Concepts in Biology

SB1: Key Concepts in Biology Paper 1 + 2 Specification: https://qualifications.pearson.com/content/dam/pdf/GCSE/Science/2016/Specification/GCSE_Biology_Spec.pdf

Compare and contrast prokaryotic and eukaryotic cells

prokaryotes:

• contains NO membrane bound organelles

  • e.g. NO nucleus, chloroplasts, mitochondria

• contains plasma membrane, cytoplasm, ribosomes, loop of chromosomal DNA

  • examples include: bacteria

eukaryotes:

• contain membrane bound organelles

  • e.g. nucleus, chloroplasts, mitochondria etc.

• examples include:

  • plant + animal cells, fungi

What is the function of a cell membrane?

• separates cell from external environment; controls passage of organic molecules, ions, water, oxygen, and wastes into and out of the cell

  • found in prokaryotes, animal + plant cells

What is the function of a nucleus?

• cell organelle that houses DNA and directs synthesis of ribosomes and proteins

  • found in animal and plant cells

What is the function of cytoplasm?

• provides structure to cell; site of many chemical reactions; medium in which organelles are found

  • found in prokaryotes, animal + plant cells

What is the function of mitochondria?

• site of aerobic respiration

  • found in animal + plant cells

What are the function of ribosomes?

• protein synthesis (where proteins are made)

  • found in prokaryotes, animal + plant cells

What is the function of a cell wall?

• protection and gives the cell structure

• made from cellulose

  • found in plant cells

What is the function of a vacuole?

• contains cell sap

• keeps the cell turgid

  • found in plant cells

How are sperm cells adapted to their functions?

• acrosome - essential for gamete fusion, particularly for binding to and penetration of the jelly coat of an egg cell

  • contains enzymes which prevents a second sperm fertilising the egg cell

• haploid nucleus - contains one set of chromosomes as it’s a gamete

• many mitochondria - release a lot of energy quickly for the movement of the cell

• long tail (flagellum) - moves side to side so the cell can “swim” forward

How are egg cells adapted to their functions?

• cell membrane hardens after fertilisation - protects the egg as it moves through the oviduct

• jelly layer hardens after the sperm cell nucleus and egg cell nuclei fuse - prevents a second sperm from fertilising the egg cell

• haploid nucleus - contains one set of chromosomes as it’s a gamete

• large store of nutrients in the cytoplasm - provide a source of energy for mitosis and growth after fertilisation

  • jelly layer surrounding the cell membrane - helps the cell burrow through the jelly like layer surrounding an egg cell

How are ciliated epithelial cells adapted to their functions?

• diploid nucleus - contains two sets of chromosomes as it’s a body cell

• fine hair like extensions to the cell membrane - sweeps from side to side to move things across the cell surface

  • lines oviducts - moves the egg cell from the ovary to the uterus

Explain how changes in microscope technology, including electron microscopy, have enabled us to see cell structures and organelles with more clarity and detail than in the past and increased our understanding of the role of sub-cellular structures

• light microscopes use visible light to illuminate specimens, allowing us to visualise cells and their components

• electron microscopes employ a beam of electrons instead of visible light

  • these microscopes have higher magnification and superior resolving power compared to light microscopes

  • have contributed to increased understanding of the role of sub-cellular structures as it allows us to find the intricacies of cells and organelles in greater depth and clarity

Convert between millimetres, micrometres, nanometres and picometres

x1000

Define an enzyme

enzyme - a biological catalyst which speeds up a reaction without being used up

• enzymes are proton molecules, and so are made up of (100-1000) amino acids which are made in protein synthesis

Explain the mechanism of enzyme action including the active site and enzyme specificity

• lock and key model

• substrates are specific and complementary to active sites

  • substrates => whatever is reacting with the enzyme

Describe how proteins turn into amino acids

• proteins are made up of (a string of) many different amino acids

• proteins are broken down into protease then into amino acids

Describe how carbohydrates turn into glucose

• carbs are made up of (a string of) glucose molecules

• amylase breaks down carb molecules into glucose

Describe how lipids turn into fatty acids and glycerol

• lipids are made up of (a string of) fatty acids and glycerol molecules

• lipase breaks down the fat molecules into fatty acids and glycerol

Explain how enzymes can be denatured due to changes in the shape of the active site

denaturation alters an enzyme’s active site shape so the enzyme is not complementary to the active site => affect its function

State the calculations for rate of reaction

Rate of reaction:

1/time

OR

(substrate used/product made)/time

Explain the effects of temperature on enzyme activity

• higher temperature generally increases the rate of reaction

  • more collisions occur along molecules, increasing the likelihood of substrate binding to the enzyme’s active site

• beyond the enzyme’s optimum temp, enzymes denature due to excessive heat

• denaturation disrupts the enzyme’s structure making it less effective

• rate of chem reactions will initially rise with temp but declines as enzymes denature

Explain the effects of pH on enzyme activity

• each enzyme has an optimum pH at which it is the most effective

• changes in pH alter the ionisation of amino acids

• altered charges affect hydrogen bonding within the protein, leading to a change in shape

• if the new shape is ineffective, enzyme activity decreases

Explain the effects of substrate concentration on enzyme activity

• at lower substrate concentrations, active sites on most enzyme molecules remain unfilled

• as substrate concentration increases, more collisions occur

• enzymes are more likely to encounter reactant molecule

• the maximum velocity of a reaction is reached when active sites are almost continuously filled

• beyond this point, further substrate increase does not boost the rate

What is the rate calculation for enzyme activity?

rate = change/time

What is the test for identifying starch? How is it completed?

iodine test:

• place a small amount (about one spatula or 1 cm³ if the sample is liquid) of the food sample on a dish

• using a dropper, add a few drops of iodine solution onto the food sample

• observe any change in the colour of the solution

  • if starch is present in the sample, the iodine solution will turn blue-black

What is the test for identifying reducing sugars? How is it completed?

benedict’s test:

• take 1 ml of the sample to be tested

• add 2 ml of Benedict’s reagent to the sample

• heat the mixture in a boiling water bath for 3 to 5 minutes

• if reducing sugars are present, a brick-red precipitate of cuprous oxide (Cu₂O) will form

  • glucose not present: remains blue

  • little bit of glucose present: clear blue => green

  • lots of glucose present: clear blue => brick red + precipitate

What is the test for identifying proteins? How is it completed?

biuret test:

• take a liquid sample of the substance you want to test for proteins

• add biuret solution A to the sample and mix it carefully

• trickle a little biuret solution B down the side of the tube

• observe the area where the two solutions meet

  • if proteins are present, a positive colour change will be from blue => purple

What is the test for identifying fats? How is it completed?

ethanol emulsion test:

• take the sample to be tested

• add ethanol to the sample and shake to mix

• transfer the mixture to a test tube containing water

• if lipids are present, a milky emulsion will form (the solution appears cloudy)

  • positive appearance change: clear => cloudy

  • more lipids present = more obvious milky solution

    • no lipids = solution remains clear

Explain how the energy contained in food can be measured using calorimetry

energy transferred (Joules) = (mass of water (g) × 4.2 J/g°C × temperature increase (°C)) ÷ mass of food (g)

Explain how substances are transported into and out of cells by diffusion

a passive process in which particles move from an area of high concentration => low concentration

• doesn’t require any energy

• how oxygen leaves a leaf

• involves transport of solutes

• follows concentration gradient

Explain how substances are transported into and out of cells by osmosis

the net movement of water molecules from a solution with high concentration to a solution with low concentration through a cell’s partially (semi) permeable membrane

• how water keeps plant cells turgid

• follows concentration gradient

Explain how substances are transported into and out of cells by active transport

the process of molecules going from a low concentration => high concentration

• requires a protein pump + energy

• against a concentration gradient

• how minerals get into a root hair cell

Calculate percentage gain and loss of mass in osmosis

percentage mass change:

(finish mass - start mass)/start mass * 100