Biology (triple content) topic 2 - Year 9

What are stem cells

Stem cells are undifferentiated cells that have the ability to become specialised cells that you need to build a human

What are the advantages with stem cells

They can be cloned and made to differentiate into specialised cells to be used in medicine or research

Help repair damaged tissues

Used to replace damaged cells

Hoped in the future to be able to grow a replacement organ from an adults stem cells = getting rid of need for a donor so no chance that body eject the donated organ

What are the disadvantages with stem cells

if not inserted properly they can lead to cancer

When grown in a lab they could get contaminated with a virus

An embryo is a human life and should not be used for experiments

What is the practical for investigating enzyme activity affected on PH

1. Blend potatoes with water and filter to make a potatoe extract full of all the catalase from the cells

2. Add this to various pH buffers and hydrogen peroxide in a test tube

3. and using a test flask fill it with water and attach a tube from the test tube to the flask and measure the bubble of oxygen produced per minute from the reaction

Method of measuring the energy content of a food sample

1. Weigh the food sample

2. Place 20cm³ of water in a boiling tube

3. Measure the temperature of the water

4. Light the food and hold it under the boiling tube

5. Continue this until it will to longer burn

6. Stir the water and measure the final temperature

There are two things you need to know to work out how much energy is in the sample =

1. Amount of joules of energy that raises the temperature of 1g of water by 1 degree

2. How much 1cm³ of water mass is

= therefore you can work out the equation for energy = (final temp - start temp) x 20 (g) x 4.2/ mass of food (g)

1. 4.2 joules of energy raises the temperature of 1g water by 1 degree

2. 1cm³ of water has a mass of 1g

What is the equation for energy 1/g

Energy in 1g = (final temp - start temp) x 20 (g) x 4.2/ mass of food (g)

How can you work out how much energy is in a food

Burn it in a calorimeter

What is the total energy content measured in

Kilojoules KJ

what is the role of diffusion in gaseous exchange for plants

1. gaseous exchange in plants occurs through the stomata in the leaves

2. the gases move by diffusion (high concentration to a low concentration)

what happens between carbon dioxide and oxygen = during photosynthesis

carbon dioxide enters the leaf

oxygen exits the leaf

what happens between carbon dioxide and oxygen = during respiration

oxygen enters the leaf

carbon dioxide exits the leaf

how is the structure of the leaf adapted for gaseous exchange

1. broad so large surface area for diffusion

2. thin so short diffusion distance

3. air spaces allow gases to easily move to all cells

4. lots of stomata

5. plants can control the opening and closing of the stomata using guard cells

what is the role of stomata in gas exchange

allow movement of gases in and out of the air spaces by diffusion

what is the method to investigating the effect of light on net gas exchange from a leaf using hydrogen carbonate indicator = start of with what the indicator does

1. hydrogen carbonate indicator starts of orange

2. if it turns purple there is low CO2 meaning photosynthesis occurred

3. if it turns yellow there is high CO2 meaning respiration occurred

4. using 4 test tubes place one leaf (all the same size) in 3 of them with all 4 having the same volume of hydrogen carbonate indicator in each one.

5. the empty one is used as a control experiment

6. wrap one tube (with a leaf in) in aluminium foil

7. wrap one tube (with a leaf in) in muslin

8. leave the remaining tubes bare

9. shine a bright light onto the tubes and leave them for 45 minutes

what is the results to investigating the effect of light on net gas exchange from a leaf using hydrogen carbonate indicator

1. the control one = indicator stays orange = no change in CO2

2. the tube covered in foil = no light = no photosynthesis could of occurred = leaf was respiring = indicator turns yellow = producing CO2

3. the tube with no cover = photosynthesis occurred = indicator turns purple = used up CO2 in the tube

4. the tube covered in muslin = had some light = no change in CO2 = indicator stays orange

how long does respiration occur in plants

24 hours

when does photosynthesis occur

during when sunlight is available

what does the net exchange of gases depend on

how much light is available

describe this graph on what happens with gas exchange during hours of the day