2b. Structure & Function in Living Organisms: Biological molecules + Movement of substances into and out of cells + Nutrition

what are the three main categories of biological molecules, and what elements do they contain?

carbohydrate: carbon, oxygen, hydrogen

protein: carbon, oxygen, hydrogen (some contain small amounts of other elements like nitrogen and sulfur)

lipid: carbon, oxygen, hydrogen

what are carbohydrates made up of? what types are there?

• they can be small, simple sugars, or more complex larger molecules

• monosaccharides are simple sugars:

  • glucose (C₆H₁₂O₆), fructose and galactose

• disaccharides:

  • maltose: glucose + glucose

  • sucrose: glucose + fructose

  • lactose: glucose + galactose

• polysaccharides:

  • starch: in plants

  • glycogen: in the liver

  • cellulose: in cell walls

  • all are made of many glucose molecules

  • polysaccharides are insoluble and therefore useful as storage molecules

what are lipids made up of? what categories are they divided into?

• triglycerides

  • glycerol + 3 fatty acids

• they are divided into fats (solid at room temperature) and oils (liquids at room temperature)

what are proteins made up of? what do they do? what are some examples?

• long chains of amino acids

• there are hundreds of thousands of different proteins

• they have different shapes, and their shape determines their function

• examples include enzymes, haemoglobin, ligaments, keratin

how would you prepare a food sample for a food test?

• break up the food using a pestle and mortar

• transfer to a test tube and add distilled water

• mix the food with the water

• filter the mixture using a funnel and filter paper

what is the test for glucose?

• add Benedict’s solution to a sample solution in a test tube

• heat in a water bath for 5 minutes

• take the test tube out of the bath and observe the colour

• positive test shows a colour change from blue to brick red

what is the test for starch?

• add drops of iodine solution to the sample

• a positive test will show a colour change from orange-brown to blue-black

what is the test for protein?

• add drops of Biuret solution to the sample

• a positive test will show a colour change from blue to violet/purple

what is the test for lipids (fats)?

• mix the food sample with 4cm³ of ethanol and shake

• allow time for the sample to dissolve

• strain the ethanol solution into another test tube

• add the solution to an equal volume of cold distilled water

• a positive test will show a cloudy emulsion forming

what are enzymes? why are they necessary to all living organisms?

proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up

they are necessary because they maintain reaction speeds of all metabolic reactions at a rate that can sustain life

how do enzymes work?

• enzymes are specific to one particular substrate, as the active site of the enzyme is a complementary shape to the substrate

• the substrate slots into the enzyme’s active site, and together they form the enzyme-substrate complex

• the enzyme catalyses the reaction and the products leave the active site as they no longer fit, and the enzyme is free to take up another substrate

what is an enzyme’s ‘optimum temperature’? what is it in the human body?

the temperature enzymes work fastest at is their ‘optimum temperature’

in the human body, it is 37⁰C

what happens when an enzyme is heated to a temperature beyond the optimum temperature?

the peptide bonds that hold the enzyme together break and the enzyme changes shape - this is known as denaturation

when the active site changes shape, the substrate can no longer fit into it and the enzyme can no longer catalyse the reaction

denaturation is irreversible

how does temperature affect enzyme’s productivity?

increasing the temperature towards the optimum increases the activity of enzymes as they have more thermal energy, and therefore more kinetic energy, so the molecules move faster and the number of collisions with substrate molecules increases, leading to a faster rate of reaction

low temperatures do not denature enzymes - they just make them work more slowly due to a lack of kinetic energy

PRACTICAL: Investigating temperature & enzyme activity

METHOD

• add 5cm³ of starch solution to a test tube and heat to a set temperature using a water bath

• add a drop of iodine solution to each of the wells of a spotting tile

• use a syringe to add 2cm³ of amylase to the starch solution and mix well

• using a stopwatch, every minute, transfer a drop of solution to a new well of iodine solution (initially, the solution should turn blue-black)

• repeat this process until the iodine solution stops turning blue-black

• record the time taken for the reaction to be completed

• repeat the investigation for a range of temperatures (from 20°C to 60°C)

RESULTS

• amylase is an enzyme which breaks down starch

• the quicker the reaction is completed, the faster the enzyme is working

• this investigation shows:

  • at the optimum temperature, the iodine stopped turning blue-black the fastest

    • this is because the enzyme is working at its fastest rate

  • at colder temperatures, the iodine took a longer time to stop turning blue-black

    • this is because the amylase enzyme is working slowly due to low kinetic energy and few collisions between the amylase and the starch

  • at hotter temperatures, the iodine turned blue-black throughout the whole investigation

    • this is because the amylase enzyme was denatured and so could no longer bind with the starch and break it down

PRACTICAL: Investigating temperature & enzyme activity

(CORMMS)

• C - change the temperature in each repeat

• O - does not apply

• R - repeat the investigation several times to ensure results are reliable

• M - measure the time taken

• M - for the iodine to stop turning black

• S - control the concentration and volume of starch solution, iodine, and amylase used

what is the optimum pH for most enzymes?

7

how does pH affect enzymes?

• if the pH is too high or too low, the bonds that hold the amino acid chaintogether can be disrupted/destroyed

• this changes the shape of the active site, so the substrate can no longer fit into it, reducing the rate of reactivity

• moving too far away from the optimum pH will cause the enzyme to denature and activity will stop

PRATICAL: Investigating pH & enzyme activity

METHOD

• add a drop of iodine solution to each of the wells of a spotting tile

• use a syringe to place 2cm³ of amylase into a test tube

• add 1cm³ of buffer solution (at a specific pH) to the test tube

• add 2cm³ of starch solution to the amylase and buffer solution. start the stopwatch whilst mixing using a glass rod

• every 10 seconds, transfer a droplet of the solution to a new well of iodine solution (which should initially turn blue-black)

• repeat this transfer process until the iodine solution stops turning blue-black

• record the time taken for the reation to be completed

• repeat the investigation with buffers at different pH values

RESULTS

• amylase is an enzyme which breaks down starch

• when the iodine solution remains orange-brown, all the starch has been digested

• this investigation shows:

  • at the optimum pH, the iodine stopped turning blue-black the fastest

    • this is because the enzyme is working at its fastest rate

• at higher or lower pHs the iodine took a longer time to stop turning blue-black or continued to turn blue-black for the entire investigation

  • this is because on either side of the optimum pH, the enzymes start to denature and as a result are unable to bind with the starch and break it down

PRATICAL: Investigating pH & enzyme activity

(CORMMS)

• C - change the pH of the buffer solution

• O - this is not relevant as we are not using an organism

• R - repeat the investigation several times to ensure results are reliable

• M - measure the time taken

• M - for the iodine to stop turning blue-black

• S - control the concentration and volume of amylase, iodine and starch solution used in the investigation

define diffusion

the movement of molecules from an area of higher concentration to an area of lower concentration

how do molecules move?

down the concentration gradient

randomly - the result of this movement is the spreading out of molecules until they are at even concentration throughout the available space

how do molecules diffuse in living organisms?

molecules move into or out of cells by diffusion when they cross the cell membrane, which is partially permeable

define osmosis

the movement of free water molecules from an area of higher concentration to an area of lower concentration through a partially permeable membrane

how does osmosis work in animal cells?

• without a cell wall, osmosis can have severe effects on animal cells:

  • in concentrated solutions, cells lose water and become crenated

  • in distilled water, the cell gains water and bursts as it lacks a cell wall to maintain structure

how does osmosis work in plant cells?

• due to the cell wall, plant cells are protected from bursting:

  • in concentrated solutions, the cell loses water, the vacuole shrinks, and the cell membrane pulls away from the wall, making the cell plasmolysed

  • in distilled water, the cell gains water, the vacuole expands, and the membrane pushes against the cell wall, making the cell turgid

    • turgid cells provide structural support and prevent wilting in plants

define active transport

the movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration

active transport requires energy because particles are being moved against the concentration gradient

how does active transport work? what are some examples?

it involves protein carrier molecules that are embedded in the cell membrane

absorption of nutrients into the bloodstream from the small intestine / absorption of mineral ions from the soil into the root hair cells of plants

what factors affect diffusion?

• surface area : volume ratio

  • great sa:v ratio → higher rate of diffusion

  • the bigger a cell or structure is, the smaller its sa:v ratio

  • cells which are adapted for diffusion have increased sa:v ratio in some way - e.g. root hair cells in plants, highly folded surface of small intestine

• diffusion distance

  • the shorter the distance molecules have to travel, the faster the rate of diffusion

  • why blood capillaries and alveoli have walls which are only one cells thick

• temperature

  • the higher the temperature, the faster the rate of diffusion

  • the molecules move faster as they have more thermal and therefore more kinetic energy

  • results in more collisions against the cell membrane

• concentration gradient

  • the steeper the concentration gradient, the faster the movement across it will occur

  • this is because on the side with the higher concentration, more random collisions against the membrane will occur

PRACTICAL: Investigating diffusion & osmosis

METHOD

• cut 2 equally-sized cubes of beetroot

  • same dimensions so they have the same SA:V ratio

• rinse beetroot

• put 5cm³ of water into 2 test tubes labelled A and B

• keep test tube A at room temperature and transfer test tube B to a hot water bath at 90℃

• leave them for 2 minutes then add a cube to each

• after 10 minutes, observe the colour of the liquid

RESULTS

• at the higher temperature, more of the pigment has leaked out

• this is because:

  • the cell membrane of the beetroot cells has become damaged so more pigment can leak out

  • at higher temperatures, particles have more kinetic energy which results in faster movement of particles

PRACTICAL: Investigating diffusion & osmosis

(CORMMS)

• C - change the temperature of the water

• O - the beetroot cubes will all be taken from the same beetroot

• R - repeat the investigation several times to ensure results are reliable

• M - observe the colour change of the liquid

• M - after 10 minutes

• S - control the volume of water used, the dimensions of the beetroot cubes and each cube will be blotted

PRACTICAL: Factors that influence osmosis

METHOD

• prepare a range of sucrose solutions ranging from 0 mol/dm³ to 1 mol/dm³

• set up 6 labelled test tubes with 10cm³ of each of the sucrose solutions

• cut 6 equally-size cylinders of potato using a cork borer and knife

• blot each one with a towel and weigh on balance

• put 1 piece into each concentration of solution

• after 4 hours, remove them, blot with paper towels and reweigh

RESULTS

• calculate the % change in mass for each potato

• the potato in distilled water will gain the most mass due to a steep concentration gradient, causing water to move into the cells by osmosis, increasing turgor pressure and making the potato firm

• the potato in the strongest sucrose solution will lose the most mass as water moves out of the cells by osmosis, making them flaccid and the potato soft

PRACTICAL: Factors that influence osmosis

(CORMMS)

C - change the concentration of the sucrose solution

O - the potato cylinders will all be taken from the same potato

R - repeat the investigation several times to ensure results are reliable

M - measure the % change in mass of the potato cylinders

M - after 4 hours

S - control the volume of sucrose solution used, dimensions of potato cylinders, each cylinder must be blotted before it is weighed

define photosynthesis

the process by which plants manufacture carbohydrates from raw materials using energy from light

what is the equation for photosynthesis?

what factors limit the rate of photosynthesis?

temperature

light intensity

co2 concentration

how does temperature affect photosynthesis?

how does light intensity affect photosynthesis?

how does co2 concentration affect photosynthesis?

what are the leaf structures?

Structure	Description
Wax cuticle	Protective layer on top of the leaf, prevents water from evaporating
Upper epidermis	Thin and transparent to allow light to enter palisade mesophyll layer underneath it
Palisade mesophyll	Column-shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis
Spongy mesophyll	Contains internal air spaces that increase the surface area to volume ratio for the diffusion of gases (mainly carbon dioxide)
Lower epidermis	Contains guard cells and stomata
Guard cell	Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in, oxygen to diffuse out
Stomata	Where gas exchange takes place: opens during the day, closes during the night. Evaporation of water also takes place from here. In most plants, found in much greater concentration on the underside of the leaf to reduce water loss
Vascular bundle	Contains xylem and phloem to transport substances to and from the leaf
Xylem	Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata
Phloem	Transports sucrose and amino acids around the plant

what mineral ions are needed in plants?

PRACTICAL: Evolution of Oxygen

METHOD

• Take a bundle of shoots from a type of pondweed

• Submerge them in a beaker of water underneath an upturned funnel

• Fix a boiling tube with water and place it over the end of the funnel

• As oxygen is produced, the bubbled os gas will collect in the boiling tube and displace the water

RESULTS

• Show that the gas is oxygen with a glowing splint

• The volume of oxygen/quantity of bubbles can be measured in order to investigate the rate of photosynthesis

PRACTICAL: Investigating Light and Photosynthesis

METHOD: PART 1

• De-starch the plant by placing it in a dark cupboard for 24 hours

  • Ensures any starch already in present in the leaves will be used up

• Partially cover a leaf of the plant with aluminium foil and place the plant in sunlight for 1 day

• Remove the covered leaf and test for starch using the method below

METHOD: PART 2

• Drop the leaf in boiling water

  • This kills the tissue and breaks down the cell walls

• Transfer the leaf into hot ethanol in a boiling tube for 5-10 minutes

  • This removes the chlorophyll so colour changes from iodine can be seen more clearly

• Rinse the leaf in cold water to soften the tissue

• Spread the leaf out on a white tile and cover it with iodine solution

what are the 7 food groups?

• carbohydrates

• proteins

• lipids

• fibre

• vitamins

• minerals

• water

what are the causes and effects of malnutrition?

what is the function of carbs?

source of energy

what is the function of protein?

growth and repair

what is the function of lipids?

insulation and energy storage

what is the function of fibre?

provides bulk (roughage) for the intestine to push food through it

what is the function of vitamins and minerals?

needed in small quantities to maintain health

what is the function of water?

needed for chemical reactions to take place in the body

what are some examples of vitamins and minerals?

calcium - strong teeth and bones

vitamin D - helps the body absorb calcium
vitamin C - forms an essential part of collagen

vitamin A - needed to make the pigment in the retina for vision

iron - needed to make haemoglobin, the pigment in red blood cells that helps to carry oxygen

who needs more energy than the average person?

• young people

• more active

• pregnant women

• breastfeeding mothers

• men

define digestion

a process in which relatively large, insoluble molecules in food are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body

label the digestive system

what are the functions of the organs that make up the digestive system?

Alimentary canal and accessory structures table

Structure	Function
Mouth / salivary glands	Mechanical digestion: teeth chew food to break it into smaller pieces and increase its surface area to volume ratio Chemical digestion: amylase enzymes in saliva start digesting starch into maltose The food is shaped into a bolus (ball) and lubricated by saliva so it can be swallowed easily
Oesophagus	The tube that connects the mouth to the stomach Wave-like contractions take place to push the food bolus down without relying on gravity
Stomach	Food is mechanically digested by churning actions while protease enzymes start to chemically digest proteins. Hydrochloric acid is present to kill bacteria in food and provide the optimum pH for protease enzymes to work.
Small intestine	The first section is called the duodenum; this is where digestion of the food exiting the stomach is completed by enzymes that are present in the duodenum lining and secreted by the pancreas The pH of the small intestine is slightly alkaline; around pH 8-9. The second section is called the ileum and is where the absorption of water and digested food molecules takes place; the ileum is long and lined with villi to increase the surface area over which absorption can take place
Large intestine	Water is absorbed from the remaining material in the colon to produce faeces Faeces are stored in the rectum and exit the body via the anus
Pancreas	Produces all three types of digestive enzymes: amylase, protease and lipase Secretes enzymes in an alkaline fluid into the duodenum for digestion; this raises the pH of fluid coming out of the stomach
Liver	Amino acids that are not used to make proteins are broken down here (deamination), producing urea Produces bile to emulsify fats (break large droplets into smaller droplets), an example of mechanical digestion
Gall bladder	Stores bile to release into the duodenum

what are the six different stages of food breakdown?

• ingestion - the taking in of substances into the body through the mouth

• mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules

• chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules

• absorption - the movement of small food molecules and ions through the wall of the intestine into the blood

• assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

• egestion - the passing out of food that has not been digested or absorbed (as faeces) through the anus

how does peristalsis work?

• Firstly, muscles in the walls of the oesophagus create waves of contractions which force the bolus along

• Once the bolus has reached the stomach, it is churned into a less solid form, called chyme, which continues on to the small intestine

• Peristalsis is controlled by circular and longitudinal muscles

  • Circular muscles contract to reduce the diameter of the lumen of the oesophagus or small intestine

  • Longitudinal muscles contract to reduce the length of that section the oesophagus or the small intestine

• Mucus is produced to continually lubricate the food mass and reduce friction

• Dietary fibre provides the roughage required for the muscles to push against during peristalsis

what are the three main types of digestive enzymes?

• carbohydrases

• proteases

• lipases

what do carbohydrases do?

• enzymes that break down carbohydrates into simple sugars such as glucose

• amylase breaks down starch into maltose

  • it is made in the salivary glands, the pancreas and the small intestine

  • amlyase from the salivary glands gets denatured in the stomach acid and must be replaced by amylase from the pancreas in the small intestine

• maltase then breaks down maltose into glucose

what do proteases do?

• they break down proteins into amino acids

• pepsin made in the stomach breaks down proteins into smaller polypeptide chains

• protease enzymes made in the pancreas and small intestine break the chains into amino acids

what do lipases do?

• break down lipids to glycerol and fatty acids

• produced in the pancreas and secreted into the small intestine

what is bile?

• bile is an alkaline substance produced in the liver

• before being released into the small intestine, bile is stored in the gallbladder

what are the two main roles of bile?

1. Neutralising the hydrochloric acid from the stomach

   • The alkaline properties of bile allow for this to occur

   • This neutralisation is essential as enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach

2. Breaking apart large drops of lipids (fats) into smaller ones (and so increasing their surface area)

   • This is known as emulsification

how is the small intestine adapted for absorption?

• very long

• has a highly folded surface with millions of villi

• these adaptations massively increase the surface area of the small intestine, allowing absorption to take palce faster and more efficiently

how are the villi of the small intestine adapted for the rapid absorption of substances?

• large surface area

  • microvilli on the surface of the villus further increase the surface available for absorption

• short diffusion distance

  • the wall of a villus is only one cell thick

• steep concentration gradient

  • the villi are well supplied with a network of blood capillaries that transport glucose and amino acids

  • a lacteal (lymph vessel) runs through the centre of the villus to transport fatty acids and glycerol

  • enzymes assist with chemical digestion

  • the movement of villi moves food along and mixes it with the enzymes

PRACTICAL: Energy Content of a Food Sample

METHOD

• use a measuring cylinder to measure out 25cm³ of water and pour it into the boiling tube

• record the starting temperature of the water using a thermometer

• record the mass of the food sample

• set fire to the sample of food using a bunsen burner and hold the sample under the boiling tube until it has completely burned

• record the final temperature of the water

• repeat the process with different food samples

RESULTS

• the larger the increase in water temperature, the more energy is stored in the sample - use the equation