Hyndland Secondary Page 1 09/10/2011

Hyndland Secondary 09/10/2011

Credit Material in italics Biology Department 1



INVESTIGATING CELLS

INVESTIGATING LIVING CELLS

Cell Structure & function

All living things are made of cells.

Microscopes are used to study the structure of cells.

The MAGNIFICATION of a microscope is found by multiplying the strength of the two

lenses together: Magnification = eyepiece X objective

Stains are coloured solutions used to show up the internal structure of cells more clearly e.g.

Iodine stains nuclei yellow.

Diagrams of Animal and Plant Cells

Similarities and Difference between Plant & Animal cells

FOUND IN BOTH PLANT AND ANIMAL CELLS

Structure Description Function

Nucleus Contains chromosomes made of DNA Controls ALL cell’s activities

Cytoplasm Clear, jelly like substance Site of cell’s chemical reactions e.g. respiration

Cell Membrane Flexible Controls what enters/ leaves the cell

FOUND IN PLANT CELLS ONLY

Cellulose cell wall

Rigid , made of cellulose Gives cell shape, prevents plant cells bursting when swollen

Vacuole large, membrane bound cavity filled with sap (watery solution of salts and sugars)

Provides support, storage

Chloroplast contains the green pigment chlorophyll traps light for photosynthesis

ANIMAL CELL PLANT CELL



WHAT YOU SHOULD NOW KNOW

Cells Investigating cells 1- State what are the basic units of all living

cells

Cells

2- Explain the purpose of staining animal and

plant cells

Stains make parts of the cell stand out so that they are

easier to see with a microscope

3-State the structure of a typical plant and

animal cell and list the differences between

them.

Plant and animal cells have in common:

1-Nucleus 2-Cell membrane 3-Cytoplasm

In addition, plant cells have:

4- Cell wall (always) 5- A vacuole (most)

6-Chloroplasts (some)



INVESTIGATING DIFFUSION

Diffusion

Diffusion is the movement of a substance from a HIGH concentration to a LOWER

concentration

Diffusion continues until the concentrations are equal.

A concentration gradient is a difference in concentration between two areas. Diffusion is said

to occur down a concentration gradient.

Importance of Diffusion

Substance needed by the cell pass INTO the cell by diffusion e.g. oxygen & dissolved food (glucose)

Waste substances pass OUT of the cell

e.g. carbon dioxide (from respiration), urea (from the breakdown of amino acids)

In the body diffusion occurs in the lungs, kidneys and small intestine:

Lungs (see S4 notes): oxygen into blood, carbon dioxide out of lungs

Kidney: useful substances e.g glucose, amino acids are reabsorbed from the tubule into the blood capillary

Small intestine : products of digestion are absorbed into the blood stream.



Cell Membrane

The cell membrane controls the passage of materials into & out of the cell

It has tiny pores (holes).

Small molecules (e.g. glucose, carbon dioxide, urea) can pass through these pores, but larger

(e.g. sucrose, starch, proteins) or charged molecules (sodium or potassium ions) cannot.

Substances which are not dissolved cannot diffuse through the membrane (e.g. carbon dioxide

and oxygen need to dissolve in a layer of mucus before diffusing into the blood from the lung

see p). In the leaf a layer of moisture is found on the spongy mesophyll cells into which

carbon dioxide diffuses.

Osmosis

Osmosis is a special case, the diffusion of water across membranes.

Osmosis = the movement of water from a higher water concentration (HWC) to a lower water concentration

(LWC) across a selectively permeable membrane*.

*The cell membrane is a selectively permeable membrane (only small molecules can pass

through them)



In the diagram below:

Water moves by osmosis from a HWC outside the bag to a LWC

inside the bag

Glucose is at a high concentration inside the bag, so diffuses out.

Starch is too large to move through the pores in the membrane so stays

in the bag.

Osmosis in Plant Cells

cytoplasm

LIQUID OUTSIDE

CELL

WATER GAIN or LOSS CHANGE to CELL

Water Cell gains water Cell swells

Solution equal to cell solution No net gain or loss of water Cell does not change

Solution stronger than cell sap Cell loses water Cell shrinks

Visking tubing (a man made material containing tiny pores). Starch and glucose solution water



When plant cells take in water by osmosis, they swell

and become TURGID.

When plant cells lose water by osmosis they become

FLACCID.

PLASMOLYSIS occurs when a cell becomes very

flaccid. So much water has been lost that the cell

membrane shrinks away from the cell wall. This

usually starts at the corners

The membrane surrounding the vacuole is also

selectively permeable and so the vacuole shrinks and

expands with osmosis.

Osmosis in Animal Cells

Animal cells contain weak solutions of salt and sugar and only have a cell membrane. Consequently they

BURST if too much pressure is placed on it.

Animal cells can gain or lose water by osmosis:

Changes in red blood cells due to osmosis

Solution outside cell Water gain or loss Change to cell

Water Cell gains water Cell swells & bursts

Solution weaker than cell solution Cell gains water Cell swells & bursts

Solution equal to cell solution No loss/ gain Cell does not change

Solution stronger than cell sap Cells loses water Cell shrinks




Investigating diffusion

4- State what diffusion is It is the movement of a substance from an area of high concentration to an area of low concentration.

5- Give examples of substances which enter

and leave the cell by diffusion Glucose, oxygen, carbon dioxide and water

6- (C) Explain the importance of

diffusion to organisms

Diffusion allows gases to move in and out of cells.

In small organisms (e.g. bacteria, amoeba), gases diffuse

through the cell membrane.

In larger organisms: most cells are not in direct contact

with air. Gas exchange takes place through specific

organs: e.g. lungs in humans, gills in fish and leaves in

plants.

7- Describe the function of cell

membrane

The cell membrane: controls the passage of substances in and out of the cell.

8- Explain what osmosis is. Osmosis is a special case of diffusion: the molecule

which diffuses across the membrane is water

9- Give the name use to describe plants

cells which have swollen up by osmosis

and those which have shrunk

swollen up: turgid shrunk: plasmolysed

10- (C) Explain osmosis in terms of a

selectively permeable membrane and of a

concentration gradient

Osmosis is the movement of water through a selectively permeable membrane (size of membrane holes

determines which molecules can go through it) along the

concentration gradient, from an area of high water

concentration to an area of low water concentration.

11- Explain osmosis in terms of water

concentration of the solution involved.

Osmosis is the movement of water through a selectively permeable membrane from an area of high

water concentration to an area of lower water

concentration.



INVESTIGATING ENZYMES

Enzymes

Within living cells many CHEMICAL REACTIONS occur. However, at body temperature

these reaction would be too slow for life to be possible. The reactions are speeded up by

enzymes which act as catalysts.

CATALYSTS:

SPEED UP chemical reactions

Remain UNCHANGED during the reaction

REPEAT the reaction over and over again

Enzymes are CATALYSTS in living cells.

Enzymes are made form PROTEIN. They perform two types of reaction:

BUILDING UP of small molecules into larger molecules

BREAKING DOWN of large molecules into small molecules.

Enzymes are needed in cells to:

Synthesise useful products

Release energy during cell respiration

Change poisonous wastes into safer materials

Change substances into a form that can be stored or used

Reactions of photosynthesis, on which all life depends.

SUBSTRATE – the substance on which an enzyme acts

PRODUCT – the substance produced by the action of the enzyme

enzyme*

SUBSTRATE PRODUCT

*The enzyme itself is not changed by the chemical reaction



Examples of Enzymes:

Name of Enzyme Where found What it Does Test for Activity

Degradation reaction (Breaking down reactions)

CATALASE In plant and animal

tissues

Breaks down

hydrogen peroxide

into OXYGEN and

WATER

Glowing splint

relights in the gas

given off

AMYLASE In digestive juices

(saliva, pancreatic

juice)

STARCH is broken

down into

MALTOSE

Benedict’s reagent

turns orange

Synthesis reactions (Building up Reactions)

PHOSPHORYLASE In potato tubers Builds special

reactive glucose

(GLUCOSE – 1 –

PHOSPHATE) into

STARCH

Iodine turns blue

black as starch is built

up

How Enzymes Work

Enzymes have a particular

shape. On their surface is

a groove called the active site

(see over). The shape of the

active allows the substrate (S) to fit into it exactly, like a key in a lock. When the substrate binds to the active

site a chemical reaction occurs.

Other molecules, because they have a different shape, cannot fit into the active site. Because of this enzymes can

work on only one substrate molecule – they are said to be SPECIFIC.

As each enzyme is specific for a single substrate molecule, a different enzyme is required for each chemical

reaction.



Effect of Temperature on Enzymes

At low temperatures enzymes work slowly –

(Their reaction rate is at a MINIMUM)

As the temperature increases, they work faster,

up to a MAXIMUM RATE.

The temperature at which an enzyme works at

its maximum rate (not best!) is called the

OPTIMUM TEMPERATURE.

Any further increase in temperature causes the enzyme protein to be damaged. The enzyme’s shape changes, so

the rate decreases again, because the enzyme no longer works.

Denaturation of enzymes

When an enzyme is unable to work because its shape has

changed it is said to be DENATURED. As the

temperature rises above the optimum, the enzyme becomes

denatured and the activity rapidly decreases to zero.

It can non longer work because the shape of the active site no

longer fits the shape of the substrate and the substrate can no

longer fit in.

The effect of pH on enzymes

An enzyme will work only in a narrow range of pH.

If the conditions become too acid or alkali, the enzyme

becomes denatured.

The OPTIMUM pH is the pH at which the enzyme

has most activity. The optimum pH is different for different enzymes. Pepsin is found in the stomach (acidic)

and so has an optimum pH which is acidic.




Investigating enzymes

20- Describe a chemical reaction in general terms A substrate is chemically altered into a product

21- Explain the meaning of the term “catalyst”.

A catalyst is a substance which speeds up the rate (i.e. the speed) of a chemical reaction without being

changed or used up.

(i.e. a catalyst is neither a substrate nor a product as it

is unaffected by chemical reactions).

22- Explain why enzymes are required for the

functioning of living cells.

A large number of chemical reactions takes place in

every living cell continuously. These are controlled by

enzymes which are catalysts produced by the cells

themselves.

The cell processes necessary for life would happen too

slowly without enzymes.

23- State what an enzyme is. An enzyme is a biological catalyst.

24- Give an example of an enzyme involved in the

chemical breakdown of a substance

C-L-A-P

- Catalase: breaks down hydrogen peroxide into water

and oxygen

- Lipase: breaks down fats into fatty acids and glycerol

- Amylase: It breaks down starch into maltose.

- Pepsin: breaks down proteins into polypeptides and

amino acids.

25- Give an example of an enzyme involved in

synthesis (building up)

Potato phosphorylase: in potatoes, joins molecules of

Glucose-1-phosphate to form starch.

26- (C) Explain the word “specific” as applied to

enzymes and their substrate

Each enzyme only works on one substrate. E.g. Amylase

only breaks down starch. Enzymes and substrates have

matching shapes like a “lock and key”.

27- State what type of molecule enzymes are. Enzymes are proteins.

28- Describe the effect of temperature on enzyme

activity

At low temperatures, enzymes do not work effectively

(molecules move too slowly). Enzymes increase the rate

of reaction (i.e. speed up) most effectively at a

temperature called the optimum. Beyond that

temperature, an enzyme becomes denaturated, i.e. it is

irreversibly damaged

29- Describe the effect of a range of pH on the

activity of pepsin and catalase

Each enzyme has a specific pH, i.e. a pH at which it

works most effectively (faster rate of reaction). Enzyme

may work at other pH but the rate of the chemical

reaction that they control is usually not as fast. Pepsin works most effectively at pH 2.8 (acidic

condition found in the stomach). It has a narrow range of

pH at which it works well (± 0.5 pH units).

Catalase works most effectively at pH 7-9 and has a

larger working range of pH than pepsin (± 1 pH units).

30- (C) Explain the term “optimum” as applied to the

activity of enzymes

The conditions at which enzymes work most effectively

are called optimum conditions: optimum pH and optimum temperature.

31-(C) Explain what a control is. A repeat of an experiment to show that the effect

observed is only due to the factor being investigated

(e.g. activity of an enzyme)



INVESTIGATING AEROBIC RESPIRATION

Need for Energy

Living cells are the site of a number of chemical reactions. Together these chemical reactions are called

metabolism. Some of these reactions release energy. Living cells need energy for:

Cell division e.g. growth & repair

Maintaining body temperature (birds & mammals)

Movement

Chemical reactions e.g. making enzymes, digesting food

RESPIRATION is the process by which cells release ENERGY from GLUCOSE. It happens in all

living cells (plant & animal) all the time.

Aerobic Respiration

Oxygen is required for aerobic respiration. Two waste products, water and carbon dioxide are

made.

Equation for aerobic respiration:

GLUCOSE + OXYGEN WATER + CARBON DIOXIDE + ENERGY

Reactants waste products useful product

The carbon dioxide released can be detected by

Turning limewater milky

Turning bicarbonate indicator from red to yellow

Aerobic respiration occurs in many small steps, each controlled by an enzyme. This allows the

energy to be released in small amounts.



The energy in food molecules such as glucose is CHEMICAL ENERGY. Green plants

capture LIGHT ENERGY and convert it into chemical energy in photosynthesis (Error!

Bookmark not defined.). Animals obtain their food from plants (Error! Bookmark not

defined.).

The quantity of energy contained in foods can be found by burning a measured mass of food

and using the heat energy released to heat a measured volume of water.

The energy content of different foods differs:

Fats contain TWICE as much energy as proteins or carbohydrates (e.g. glucose & starch)

Respirometers

A respirometer can be used to measure the rate of respiration

The use of respirometers depends on three factors:

The volume of oxygen used up is equal to

the volume of carbon dioxide produced

The carbon dioxide can be absorbed by a

chemical (e.g. soda lime, potassium

hydroxide) and so the uptake of oxygen is

seen as a drop in the volume of air in the

respirometer

There is no change in the temperature of the

apparatus. (changes in temperature cause

changes in the volume of gases!)

In the apparatus above, the taps are closed at the start of the experiment. As the oxygen is

removed the volume of air in the tube decreases and this sucks the coloured liquid up the tube

towards the earthworm’s tube.



The control should be a non respiring material (i.e. dead animal or glass beads) and of the

same volume as the respiring animal.

The syringe is used to return the volume back to its original level. In this way, the volume of

oxygen taken in can be measured and if the time taken to produce the change is known, the

rate of respiration (oxygen uptake per minute) can be calculated.

Energy release

During respiration some of the energy is released as heat energy. As a result in a confined

space the temperature of the surroundings is raised. The heat can be detected using an air

thermometer.

The heat released by the

respiring animal expands the air

in the tube and pushes the

coloured liquid. There is no

expansion in the control side.



Investigating aerobic respiration

31- State three reasons why living cells need

energy.

Cell division, movement (muscle cells),

synthesis reactions.

32- Give an example of an energy

transformation in a plant and in an animal.

Plants: light energy → chemical energy

(starch)

Animal: chemical energy (fat) → heat energy

33- State what cells need in order to release

the energy from food.

Cells need oxygen (found in air) to release the energy from food in “aerobic respiration”

34- Describe aerobic respiration in terms of a

word equation

glucose + oxygen → energy + carbon dioxide +

water

35- State where the carbon dioxide released

from food comes from.

The carbon dioxide released as a waste product of respiration comes from food.

36-State what is produced by respiration in

addition to carbon dioxide

Heat energy and water will be produced by

aerobic respiration.

37- (C) State which type of food contains more

energy per gram: proteins, fats,

carbohydrates.

Fats contain about twice as much energy as

proteins and carbohydrates (sugars, starch)

38- (C) Explain the importance of the energy

released from food during respiration to

the metabolism of cells.

Cell metabolism is all the chemical reactions

(i.e. breakdown as well as synthesis reactions)

which take place inside a cell. The energy

released from food is needed for many

chemical reactions and therefore it is needed

for cell metabolism.



PROBLEM SOLVING

Percentage Calculations. PERCENTAGE CALCULATIONS

3 Types of percentage calculation can be asked:

Percentage change (increase or decrease):

If the answer is negative the factor has decreased, if it is positive the factor has increased

e.g. Calculate the percentage change in blood flow to the skeletal muscles during exercise, if it rises from 10 l/min to 30l /min.

Percentage change = 30-10 ÷ 10 X 100 = 20÷10 X 100 = 200% change (increase).

Percentage of: This asks what percentage a subset is of the total

e.g. What percent of the whole population has blood group AB?

Total = 24 + 45 + 33 + 86 = 188

Subset = 33

Percentage = 33 ÷ 188 X 100 = 17.6%% How many, if the percentage is already given:

e.g. If 20% of a class of 40 have blue eyes, how many of the class has blue eyes?

Total =40

Number = 40 X 20 ÷ 100

= 800 ÷ 100 = 8

Percentage change = End value—start value

Start value

X 100

To find the

change

To change to a

percentage

STEP 1 - Find the START Value (in the question)

STEP 3 - FIND OUT HOW MUCH IT HAS CHANGED

(use a calculator!!!!!): END VALUE – START VALUE

STEP 2 - Find the END value (in the question)

STEP 4 - Divide this answer by the START VALUE

STEP 5 - Multiply that answer by 100

STEP 1 - Find the START Value (in the question)

STEP 3 - FIND OUT HOW MUCH IT HAS CHANGED

(use a calculator!!!!!): END VALUE – START VALUE

STEP 2 - Find the END value (in the question)

STEP 4 - Divide this answer by the START VALUE

STEP 5 - Multiply that answer by 100

Percentage of = Size of subset

Total To change to a

percentage X100

To calculate the proportion the sub-

set forms of the total

Number = Total X Percentage

100

Blood Group A B AB O

Number 24 45 33 86



Ratios

A ratio is a way of showing the relationship between two or more values.

For example a forest contains two types of deer, Roe deer and Fallow deer. The deer are counted and

360 Roe deer are found, but only 120 Fallow deer are present. To express this as a ratio a number of

steps can carried out.

1. Try to divide the large number by the small number 360 : 120 each by 120

3:1 this is the simplest whole number ratio.

Second example.

The head teacher wishes to know the ratio of male staff to female staff in the school. There are 32

male staff and 56 female staff

1. Try to divide the large number by the small number 32: 56 each by 32

1:1.75, not a whole number ratio so move to next step

2. Divide both sides by the largest number which goes in evenly,

32:56 each by 4

8: 14 each by 2

4:7 This is the simplest whole number

ratio, the two numbers cannot be divided evenly by the same number!

Third example

The EU fishery minister suggested that the North Sea contained very little cod, but much more

herring. The survey shows that there were 175 cod, and 1,260 herring. What is the ratio of cod:

herring.

1. Try to divide the large number by the small number 175 : 1260 each by 175

7.2:1, not a whole number so move to next step

2.Find a number that will divide evenly into both sides (the same number for each side)

175: 1260 each by 5

35:252 can they be divided again?

35:252 each by 7

5:36 This is the simplest whole

number ratio, the two numbers cannot be divided evenly by the same number!



Chemical Tests TESTS

pH Scale (Acidity/ Alkalinity)

The pH Scale gives a measure of how acidic or alkaline a solution is:

pH is measured using pH indictor or paper

The pH falls (becomes more acidic) when fats are broken down to fatty acids (& glycerol), or protein

are broken down (to give amino acids)

Carbon Dioxide

Carbon dioxide is the gas used up in photosynthesis and produced in aerobic respiration in animals and

plants (along with water) and in anaerobic respiration in plants (along with alcohol). In experiments it

can be absorbed by soda lime or potassium hydroxide.

Carbon dioxide turns limewater milky.

Bicarbonate indicator can be used to tell how much carbon dioxide is present

Experimental Design

In a scientific experiment a test is only fair if only one variable factor has been changed at a time.

Examples of variable factors are time, lengths, volumes, weights and concentrations. If more than is

changed between experiments the test is not fair. A fair test is also a VALID test.

Experiments are repeated to make them more RELIABLE or REPRESENTATIVE. To make an

experiment more accurate better equipment must be used e.g. a more accurate balance or replace a ruler having centimetre divisions with one having millimetre divisions.

Food Tests

pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14

COLOUR of

pH indicator RED ORANG YELLOW

GR

EE BLUE PURPLE

Carbon Dioxide Zero Normal (0.03% High

Colour of Bicarbonate Indicator Purple Red Yellow

Food Type Reagent Procedure Positive result

Glucose (sugar) Benedict’s Heat with sample at 95°C Turns from blue to orange

Starch Iodine Add to sample Turns from orange to blue/

black

Protein Biuret Heat with sample Turns from to violet

Fats Alcohol and

water

Shake with sample. Solution goes cloudy

one is



Charts/Graphs CHARTS

In Biology two types of chart are used: the BAR chart and the LINE GRAPH

Usually a question tells you which to draw.

BAR CHART

When data concerns the numbers in various groups, then a bar chart is used

Label; axes names and units (if any)

copy the column headings. The first set of information goes on the horizontal axis, the

second on the vertical axis.

Devise a scale (divide the axis up evenly).

Find the highest value in your data. 37

Count the number of large squares on your vertical axis 8

Divide the highest value by the number of squares, 37/8 = 4.625

round your answer up to the nearest easy* number. i.e. 5 Each large square is worth 5 *easy numbers are usually 1, 2, 5, 10, 50, 100 etc.

Draw the bars (you should make each bar the same width and leave a gap between the bars (you won’t

lose marks if you don’t)

LINE GRAPH Line graphs are used when both sets of data are numbers. A scale must be used on both axes.

Label axes by copying the column headings (first 1st—horizontal, 2nd column—vertical)

Devise scales for both axes

Horizontal 50/10 = Each big box is worth 5 ºC

Vertical 74/8 = 9.25, Each big box is worth 10%

Plot the points and join with a straight line (Only join 0,0 if that point is in the data)

Colour of Flower Number

RED 37

BLUE 15

YELLOW 7

WHITE 3

GREEN 24 Nu

mber

Colour of Flower

40

35 30

25

20 15

10 5

0

RE

D

BL

UE

YE

LL

OW

WH

ITE

GR

EE

N

Temperature (ºC) Germination (%)

0 7

10 24

20 59

30 74

40 37

50 2

Ger

min

atio

n (

%)

Temperature (ºC)

80

70 60

50

40 30

20 10

0

0 10 20 30 40 50


GLOSSARY

Active Site part of an enzyme molecule to which the substrate attaches

Amylase an enzyme which speeds up the breakdown of starch

Atom the smallest part of an element which can exist chemically

Catalase an enzyme which speeds up the breakdown of hydrogen peroxide

Catalyst a substance which speeds up a reaction but remains unchanged

Cell wall cellulose layer around the outside of a plant cell

Chloroplast structure within a plant cell which contains chlorophyll

Concentration the number of solute molecules in a specific volume of solvent

Concentration Gradient the difference between two concentration levels

Cytoplasm the fluid part of a cell

Denatured permanent damage caused to an enzyme by high temperature

Diffusion movement of molecules from high to low concentration

Distilled water pure water consisting of 100% water molecules

End product(s) compound formed at the end of a reaction

Enzyme chemical found in living cells which acts as a catalyst

(Cell) Membrane selectively-permeable layer surrounding the cytoplasm in all cells

Molecule two or more atoms joined together by chemical bonds

Nucleus control centre of a cell

Optimum conditions conditions in which an enzyme works most efficiently

Osmosis diffusion of water molecules across a semi- permeable membrane

Pepsin an enzyme which breaks down protein

pH a measure of acidity/alkalinity

Phosphorylase an enzyme which synthesizes starch

Selectively permeable allows some molecules to pass through but not others

Solute substance which is dissolved in a liquid

Solvent liquid used to dissolve another substance

Specific Activity each enzyme only acts on one substrate

Stain coloured dye used to show up cell structure more clearly

Substrate the molecule on which an enzyme works

Synthesis building up a larger molecule

Vacuole cavity in the cytoplasm of a plant cell

Hyndland Secondary Page 1 09/10/2011

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