Preliminary Biology - Synergy Education · - For nearly every experiment you perform in HSC biology, you should be able to identify the variables involved, perform a risk assessment,

Preliminary Biology Notes

Module 1: Cells as the Basis of Life

Part 2 of 2

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1. Cellular Function Inquiry question: How do cells coordinate activities within their internal environment and the external environment?

Diffusion and Osmosis:

• Diffusion and osmosis are two forms of passive transport - Passive transport means no energy is required for the movement of materials

to occur

• Passive transport is ALWAYS the movement of molecules from an area where they are in high concentration to an area where they are in low concentration.

- This is referred to as movement down a concentration gradient.

• The molecules will move down the concentration gradient until they reach equilibrium - Equilibrium is when the forces pushing molecules one way balance the forces

pushing them the other way!

• Investigate the way in which materials can move into and out of cells, including but not limited to: - Conducting a practical investigation modelling diffusion and osmosis (ACSBL046) - Examining the roles of active transport, endocytosis and exocytosis (ACSBL046) - Relating the exchange of materials across membranes to the surface-area-to-

volume ratio, concentration gradients and characteristics of the materials being exchanged (ACSBL047)





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• Osmosis involves strictly the movement of water across a semi-permeable membrane - Water will move from where it is most concentrated to where it is least

concentrated until equilibrium is reached.

- In beaker ‘A’ water is in lower concentration on the right of the membrane as concentration can be thought of as:

𝑛𝑜. 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠

𝑡𝑜𝑡𝑎𝑙 𝑛𝑜. 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 %

- On the left of beaker ‘A’ water is in 100% concentration, but on the right, it is

lower, so water moves from the left to the right - When discussing osmosis we will often describe solutions as hypertonic,

hypotonic, or isotonic - These terms are used when considering a cell inside a solution – such as our

body cells!

• A hypertonic solution has a lower concentration of water compared to the internal environment of the cell

- This means there will be net movement of water by osmosis out of the cell.

• A hypotonic solution has a higher concentration of water compared to the internal environment of the cell

- This means there will be net movement of water by osmosis into the cell.

SYNERGY SUCCESS TIP: You can remember that a hypotonic solution has a higher concentration of water because it will cause the cell to swell like a hippopotamus as water moves down the concentration gradient, into the cell.





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• An isotonic solution has an equal concentration of water and solutes internally and externally

- This means there will be no net movement of water or solutes.

• Diffusion is the movement of any molecules along a concentration gradient! - If the membrane in the diagram above was also permeable to salt, the

equilibrium would look like this:

- This is because the salt molecules would diffuse across the membrane





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Practical Investigation: There are tonnes of experiments you can do to model diffusion and osmosis! At Synergy, these are the experiments we do in class:

• Modelling diffusion:

1. Fill a piece of dialysis tubing with a tablespoon of corn starch and 50mls of water. Tie off the bag or secure with a clip.

2. In a beaker, place 300mls of water and 3 drops of Lugol’s iodine. This should turn the water a murky brown/orange.

3. Place the corn starch filled tubing into the beaker and record any observations after 25mins

- Because the Lugol’s iodine is in much higher concentration outside of the plastic bag than inside, the iodine diffuses into the dialysis tubing

- When iodine comes in contact with starch, a chemical reaction occurs, changing the colour of the iodine to dark purple/black.

• Modelling osmosis:

1. Cut a potato into 5 cubes measuring 2cm x 2cm x 2cm 2. Weigh each cube and record this. 3. Place each cube into a separate beaker. 4. Fill the first beaker with about 200mls of pure water – if the potato cube is not

completed covered, add another 100mls of water. 5. Repeat this with the remaining beakers using a 1%, 5%, 10%, and 25% sucrose

solution 6. Let these sit for 1-2 hours, then remove the potato cubes, blot with paper towel to

remove excess solution and reweigh each cube 7. Using these results, create a graph of the change in mass as a percentage on the

percentage sucrose solution.

- On your graph, you should notice that some of the potato cubes lost mass, some remained relatively unchanged, and some had a mass increase

- This is because the solutions ranged from hypertonic to hypotonic, demonstrating that water moved into and out of the cell by osmosis





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• Good experimental practice: - For nearly every experiment you perform in HSC biology, you should be able

to identify the variables involved, perform a risk assessment, and explain why your results were/were not expected.

- As an example, let’s use the osmosis practical - Every risk assessment you create should follow this format:

- Independent variable (the variable that is changed): the concentration of the

sucrose solutions - Dependent variable (the variable that is measured): change in mass as a

percentage - Controlled variables: volume of solution, size of the potato cube, time that

the potato spent in the solution, etc.

Risk – What is dangerous?

Harm – Why is it dangerous?

Prevention – What can we do to stop this?

Lugol’s iodine Skin irritation and

staining Eye irritation

Wear gloves Wear safety goggles

Quickly clean up spills with high-grade

disinfectants





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Endocytosis and Exocytosis:

• Active transport is the movement of molecules against a concentration gradient, in order to accomplish this, energy must be used.

• Without active transport, organisms would not be able to effectively move necessary materials into and out of their cells

- Substances such as glucose, and salts and ions cannot passively move across the membrane, so active transport is used.

• Endocytosis is the process of capturing and engulfing substances from the external environment, and internalising it in the form of a vesicle.

- There are two types of endocytosis: phagocytosis and pinocytosis - Phagocytosis involves the cell membrane extending outwards and

enveloping large macromolecules. - Pinocytosis involves the formation of small pits which water and dissolved

substances fill and then the membrane internalises by forming a vesicle

- Endocytosis is occurring constantly in eukaryotic cells, and is how most single

celled organisms acquire food - This process however, depletes the plasma membrane.

• Exocytosis describes the process of vesicles fusing with the plasma membrane, releasing their contents to the external environment

- Exocytosis is how cells remove wastes and toxins - When exocytosis occurs, the plasma membrane is replenished as the vesicle

membrane fuses with the cellular membrane.





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Rates of Material Exchange: Concentration gradients:

• The rate at which materials will diffuse depends on the “steepness” of the concentration gradient.

- The higher the difference in concentration, the faster the rate of diffusion (by Fick’s Law)

• A graph of the rate of simple diffusion on the concentration gradient would therefore look something like this:

- This means that over time, as molecules begin to diffuse, the rate at which they diffuse decreases.

• In facilitated diffusion, the movement of materials is a lot faster, but is dependent on the amount of carrier proteins available to transport materials. A similar graph for facilitated diffusion would look like this:

- The rate of movement begins to plateau as no free carrier proteins are available to move substances





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Properties of materials:

• Some properties and characteristics of materials alter the rate at which substances can be transported and can even stop them from being transported at all!

• Some substances can’t move through the plasma membrane without the assistance of carrier/transport proteins.

- This may be because of the size of the material. e.g. oxygen, which consists of just 3 atoms, can easily move through the membrane, but glucose which is composed of 24 atoms requires active transport.

• Using the example of a drop of coloured dye in water: - Each molecule of dye has energy, causing it to vibrate and knock into other

molecules - When the molecules collide, they rebound and spread out, until they collide

with another molecule – causing these to rebound and spread out - This is a fairly accurate representation of diffusion, and will help you to

understand how size and temperature affect the rate of diffusion

• Temperature: - When heat is applied to molecules, the heat energy causes the molecules to

vibrate faster - When molecules are vibrating faster, they experience more high-energy

collisions, causing them to spread out faster - This results in the rate of diffusion increasing - Similarly, when molecules are in low temperatures, they collide with less

energy and so diffusion is slower.

• Size: - Smaller molecules diffuse at a faster rate than large molecules as they move

quicker than large molecules.

• Charged particles: - Charged substances such as ions have trouble crossing the phospholipid

bilayer, as they are more attracted to the polar external layers than the nonpolar internal layers of the membrane

• Surface area to volume ratio: - The greater the amount of surface area, the more potential for materials to

cross the membrane. - Surface area to volume ratio is a measure of how effectively a cell allows

materials to cross its membrane and distribute throughout the cell - Surface area to volume ratio is one of the biggest reasons why our cells must

be small to be effective - As volume of the cell increases, its surface area:volume ratio decreases,

making the cell less effective at the transportation of materials.





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Photosynthesis:

• Photosynthesis is the process by which plants and some algae produce ‘food’. - Rather than hunting or gathering food like animals, plants are what is known

as autotrophs. - Photosynthesis is a very complicated process that uses the radiant energy of

the sun, and some organic compounds like carbon dioxide - The process can be defined by the following equation:

• Photosynthesis occurs in two stages – the light-dependant and the light-independent (or dark stage).

- During the light-dependant stage, the radiant energy of the sun is utilised to split the water molecule, producing some chemical energy.

- The chemical energy produced is then used in the dark stage to combine the hydrogen and the carbon dioxide molecules

- This results in the formation the carbohydrate 𝐶6𝐻12𝑂6, commonly known as glucose or sugar.

• Investigate cell requirements, including but not limited to: - Suitable forms of energy, including light energy and chemical energy in complex

molecules (ACSBL044) - Matter, including gases, simple nutrients and ions - Removal of wastes (ACSBL044)

• Investigate the biochemical processes of photosynthesis, cell respiration and the removal of cellular products and wastes in eukaryotic cells





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• Chloroplasts are specialised organelles found in photosynthesising organisms - Chloroplasts consist of many granum (stacks of thylakoids) and the thylakoid

membranes are where the pigment chlorophyll is stored. - This is where the light-dependant reactions of photosynthesis occur - The pigment chlorophyll absorbs light energy in the red, orange, blue, and

violet spectrum, reflecting most green light - This is why we see plants leaves as green!

- Once the light-dependent reactions have occurred, enzymes inside the

stroma catalyse the light-independent reactions - The following is a summary of the process of photosynthesis:





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Cellular Respiration:

• Cellular respiration is the process by which nutrients are broken down to produce adenosine triphosphate (ATP), the usable energy form for all living organisms.

- Glucose is a vital component of cellular respiration needed to produce ATP. - Different organisms however, produce ATP in different ways - In organisms who respire aerobically (with oxygen) the chemical equation is

as follows.

𝐶6𝐻12𝑂6 + 6𝑂2 → 6𝐶𝑂2 + 6𝐻2𝑂 + 36 𝐴𝑇𝑃 𝑔𝑙𝑢𝑐𝑜𝑠𝑒 + 𝑜𝑥𝑦𝑔𝑒𝑛 → 𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑤𝑎𝑡𝑒𝑟 + 𝑒𝑛𝑒𝑟𝑔𝑦

- The waste products of this reaction are the same products needed for plants

to photosynthesise, and the products of photosynthesis are needed for cellular respiration.

- This is referred to as the biological energy cycle:





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• There are other forms of cellular respiration, such as fermentation and lactic acid producing respiration.

- These forms are utilised when cells do not have access to oxygen (anaerobic) - In animals, this may occur during/after intense exercise. - When our muscle cells are active, they use up all of the stored energy and

cannot produce enough energy to continue moving quickly - In this case the formula for cellular respiration becomes:

𝐶6𝐻12𝑂6 → 2𝐶3𝐻6𝑂3 + 2 𝐴𝑇𝑃 𝑔𝑙𝑢𝑐𝑜𝑠𝑒 → 𝑙𝑎𝑐𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 + 𝑒𝑛𝑒𝑟𝑔𝑦

- The waste product lactic acid then builds up in cells, responsible for the

burning or heavy sensation one feels during exercise. - The lactate remains there until it can be broken down or oxidised to be used

in the aerobic energy cycle when more oxygen is available!

- Some organisms cannot break down lactic acid, such as plants or fungi - When these organisms cannot supply enough oxygen to meet their cellular

requirements, they use a form of respiration known as fermentation - The chemical equation for this form of anaerobic respiration is:

𝐶6𝐻12𝑂6 → 2𝐶2𝐻5𝑂𝐻 + 2𝐶𝑂2 + 2 𝐴𝑇𝑃 𝑔𝑙𝑢𝑐𝑜𝑠𝑒 → 𝑒𝑡ℎ𝑎𝑛𝑜𝑙 + 𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑒𝑛𝑒𝑟𝑔𝑦





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Enzymes:

• Enzymes are proteins that organisms use to catalyse chemical reactions - Catalyse means to cause or accelerate - They do this by decreasing the amount of energy needed to begin a

reaction, called the activation energy.

• Every protein has a specific shape and composition that makes it ideal to its function

- Every enzyme is specific to the reaction it catalyses

• Enzymes act on substrates (reactants) to form the products - An enzyme-catalysed reaction can either break apart molecules of the

substrate, or combine them - Enzymes are referred to as specific because the reaction occurs on an active

site, which fits together like a puzzle piece with only one substrate-complex. - Once an enzyme has catalysed a reaction, the enzyme and substrate break

apart and the enzyme can catalyse another reaction

• Investigate the effects of the environment on enzyme activity through the collection of primary or secondary data





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• Conditions in the chemical environment can change how active enzymes are - Any deviation from the optimum conditions causes a decrease in enzyme

activity! - These conditions include the concentration of enzymes, reactants, and the

products, the temperature of the enzymes, the pH of their surroundings, and whether any inhibitors are present.

Concentration:

- Enzymes are not destroyed or damaged when they catalyse chemical reactions, so they can continue catalysing reactions basically indefinitely.

- However, each enzyme can only catalyse one reaction at a time! - This means that the more enzymes there are in a solution, the higher the

overall enzyme activity! - Similarly, reactions cannot occur if there are not enough reactants.

SYNERGY SUCCESS TIP: If this is confusing, you can think about this as a speed-dating event! Imagine 30 men show up and are seated waiting for the dates to begin, but only 10 women attend! 20 men (the enzymes) are left waiting for that chemistry, but all the women (the substrates) are having chemical reactions!





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Temperature: - Heat affects the kinetic energy of molecules, causing them to move or vibrate

faster. - If the enzyme and substrate molecules are moving around faster, contact is

more likely to occur, and the rate of activity will increase!

- However, because enzymes are proteins, they can be denatured by extreme heats.

- Denatured means the heat has destroyed some of the bonds between the atoms of the protein, causing it to change shape.

- A drastic change in pH therefore means the enzyme will no longer be able do

its job and catalyse reactions, decreasing the rate of reaction





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pH: - pH is a measure of the concentration of H+ ions! These are the ions that form

bonds between atoms in proteins! - This means pH can really affect the shape of proteins, by breaking or creating

new hydrogen bonds - When these bonds are broken, the shape of the active site changes, meaning

the enzyme can no longer catalyse reactions - To make sure all the chemical reactions in our body occur effectively, each

enzyme, depending on its role, has a different optimum pH.

- For example, pepsin is found in our stomach, which is very acidic, and so has

a very low optimum pH

Enzyme practical: - Use the following simulation to investigate the effect of pH, temperature,

and enzyme/substrate concentration on the rate of activity! - https://sites.google.com/site/biologydarkow/lactase-enzyme-simulation

https://sites.google.com/site/biologydarkow/lactase-enzyme-simulation

Documents

Preliminary Biology - Synergy Education · - For nearly every experiment you perform in HSC biology, you should be able to identify the variables involved, perform a risk assessment,