LEVEL: NATIONAL 5 Biology

Unit CELL BIOLOGY UNIT

Topic

Why are cells different from their environments?

Experiences and Outcomes

SCN 3-13a Using a microscope, I have developed my understanding of the structure and variety of cells and of their functions.

Approximate Timing

10 x1 hours

Guidance for writers:-o Please use this format to ensure consistency across the

authorityo Anything produced should be electronic to allow ease of

sharingo Please use font Times New Roman, size 12 for all work

Concept Development

Experiences and Outcomes:-

SCN 3-13a Using a microscope, I have developed my understanding of the structure and variety of cells and of their functions.

National 4

Cell Biology Unit: How do cells exchange materials? (diffusion of glucose, oxygen, carbon dioxide and water & importance of diffusion)

Pupils should be able to……

Suggested Activities Possible Resources(to include Technician guides/risk assessments, AifL techniques, any existing worksheets, references to S Grade/Int 1 textbooks where appropriate *)

Know that different concentrations of substances exist between cells and their environment.

Be able to link photosynthesis and respiration (in terms of raw materials and products)

Substances move between cells – why and how?Brainstorm to recap/build on existing knowledge to cover the following points1. Different cells require different substances2. What is outside of the cell?3. Raw materials and products- link different

cells having different functions e.g. red blood cell to carry oxygen, leaf cell to carry out photosynthesis, yeast cells making alcohol etc

4. How do these substances get in and out of the cell?

5. Visking tubing as an example of a membrane

o Experiments with Visking tubing o E.g. Starch suspension and glucose solution

inside tubing, water surrounding–test water for presence of glucose

Know that the cell membrane is not a rigid structure.

Know that the cell membrane consists of fats and proteins.

1. Recap previous lesson2. Chemical composition of the cell

membrane

o Experiment with beetroot/red cabbage in alcohol, distilled water at high temperature to illustrate membrane composition. Measure absorbance of pigment leakage using a colorimeter (as per experiment for Higher Biology)

o Website

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ap1101

o Rocket Biology CD-ROMKnow that the cell membrane is selectively permeable.

Know that substances can move across membranes passively or actively.

What is selectively permeable?1. Recap on chemical composition of the cell

membrane2. Carry out experiments to demonstrate

selectively permeable3. Consequence of membrane being

selectively permeable is being able to have different concentrations on either side of the membrane

o Experiments with Visking tubing o Starch suspension inside and dilute iodine

solution outside (the starch goes blue black- why?)

o Starch suspension and glucose solution inside and distilled water outside (record change in mass) Int 2 experiment

Know that passive movement is with the concentration gradient and does not require energy.

Be able to describe diffusion in terms of the concentration gradient and why it is important to cells.Be able to give examples to include glucose, carbon dioxide, oxygen and amino acids

Passive Movement along a concentration gradient1. What is a concentration gradient?2. Experiment to demonstrate3. Examples of diffusion involving cells

o Mesophyll cells - carbon dioxide, o red blood cells - oxygen, o yeast cell - glucoseo any cell to make protein - amino acids

o Experiments with Visking tubing with different concentrations of glucose or sucrose or salt solution inside and outside the tubing- measure change in mass – Int 2 and Higher experiment

Describe the effect of different concentrations of solute on plant tissue

Recap on concentration gradient and names of substances that can move by diffusionMovement in and out of plant tissues

o Beetroot or red cabbage in different concentrations of solute, measure colour intensity using a colorimeter.

Be able to describe osmosis in terms of net movement of water molecules across a

Movement of water as a special case of passive movement

o Experiments with Visking tubing showing osmometer (see Appendix 1)

membrane.

The terms isotonic, hypotonic, hypertonic, osmotic potential and water potential need not be used.

1. Recap concentration gradient and term passive

2. Experiment to demonstrate osmosis as a special case of diffusion, passive movement of water

Know the effects of osmosis on plant cells.Be able to describe the effects of different concentrations of solutions on plant cells.

Be able to describe what turgid and plasmolysed means

Osmosis in individual plant cells o Recap of osmosis as a special case of

passive movemento Apply this to plant cells in red

onion/rhubarb petioleo Use of turgid and plasmolysed

o Experiments with red onion cells/rhubarb petiole in distilled water and 20% sucrose solution – observe under microscope

Know the effects of osmosis on animal cells.Be able to describe the effects of different concentrations of solutions on animal cells.

Osmosis in animal cells1. Experiments with hard boiled eggs minus

their shell in syrup/water2. Effects of osmosis on red blood cells and

so need for rehydration.

o Experiments with hard boiled eggs minus their shell in syrup/waterhttp://www.practicalbiology.org/areas/intermediate/exchange-of-materials/osmosis/investigating-osmosis-in-chickens-eggs,46,EXP.htmlAvailable as a word document too see Appendix 2

Describe some applications of osmosis in real life situations for power generation and desalination

Big picture applications of osmosis1. Recap osmosis in plant and animal cells2. Following could be done as mini research-

e.g. each group researching each application- enterprise or setting up mini companies

o Generating power in Norway using osmosis. New scientist article

o Low carbon economy articleo Reverse osmosis and desalination article

Suggested websites for informationo New scientist article:

http://www.newscientist.com/article/dn18204-first-osmosis-power-plant-goes-on-stream-in-norway.html

o Low carbon economy article: http://www.lowcarboneconomy.com/profile/the low_carbon_economy_ltd/_low_carbon_blog/osmosis_purifies_water_generates_electricity/3943

o Reverse osmosis and desalination article:

http://science.howstuffworks.com/reverse-osmosis.htm

Know that active transport requires energy for the membrane proteins to move molecules against the concentration gradient and maintain the gradient.

Against a concentration gradient- Active transport1. Requires energy & against a concentration

gradient

o Experiment with yeast cells and Congo red dyehttp://www.indianastandardsresources.org/admin/library/active_yeast.pdf Also in Appendix 3

o Active transport animationshttp://www.northland.cc.mn.us/biology/biology1111/animations/transport1.html

* any additional resources produced should be attached to this file or as appendices if appropriate.

Suitable Homework and Assessment Questions

Question number Source

1 SQA Higher 2004 Q2 (all except Q2 (b) (i)

2 SQA Paper Standard Grade Credit 2004 Q9

3 SQA Paper Standard Grade Credit 2007 Q7 (part of)

Question 1 (SQA Higher 2004 Q2 (all except Q2 (b) (i))

2 marks

1 mark

1 mark

1 mark

2 marks

SQA Higher 2004 Q2 (all except Q2 (b) (i)

Question 1 Markscheme from SQA.

All questions used in the same order as SQA document. Qu 2(b)(i) omitted.

Question 2 (SQA Paper Standard Grade Credit 2004 Q9)

Question 2 Markscheme

Question 3 (SQA Paper Standard Grade Credit 2007 Q7 (part of))

Question 3 Markscheme

Appendix 1

Experiment. Osmometer

(a) Use a dropping pipette to fill the visking tubing and connector with syrup solution (Fig. I).

(b) Push the capillary tube into the connector far enough to bring the syrup to a level somewhere in the lower third of the capillary (Fig. 2).

(c) If there are short columns of liquid and air bubbles trapped in the upper part of the capillary, squeeze the visking tubing to force the syrup to the top of the capillary and then let it return slowly.

(d) Clamp the capillary tube vertically in a stand and then lower it to immerse the visking tubing in a beaker or jar of water until it is completely covered but not touching the bottom of the vessel .Leave for a minute so that the syrup can acquire the temperature of the water .

(e) Move the rubber band on the capillary to mark the level of the liquid.

(f) Watch the level of the liquid in the capillary. If it falls rapidly, examine the visking tube through the side of the beaker to see if syrup is escaping.Measure any change in level after 10 minutes.

Fig.1

Fig 2

Fig 3

capillary tube

marker atfirst level

water

Appendix 2

Investigating osmosis in chickens’ eggs

The purpose of this activity is: to observe the effect of different concentrations of sodium chloride on a de-

shelled chicken’s egg to explain the effects in terms of osmosis.Procedure SAFETY: Wear eye protection in case any of the sodium chloride solution gets in your eyes.Investigationa Ensure the egg is dry by gently patting it with a paper towel.b Place the egg on a balance and record the mass in a suitable table.c Put the egg in a 200 cm3 beaker.d Pour in enough sodium chloride solution to cover the egg. Record the

concentration of sodium chloride you have used.e Leave the egg until next lesson – at least 24 hours.f Pour the sodium chloride solution off the egg.g Dry the egg carefully using a paper towel.h Place the egg on the balance and record the mass in the table.i Calculate change in mass and percentage change in mass. j Compare the results for the different concentrations of sodium chloride.

QUESTIONS1 Why was the shell of the egg removed?

2 Why did you dry the eggs with a paper towel before weighing them?

3 Why is it a good idea to compare the percentage change in the mass of each egg, rather than the simple change in mass?

4 What happened to the egg placed in the 20% sodium chloride solution?

5 Explain why the mass of the egg changed in this way.

6 What happened to the egg in distilled water or 0% salt solution?

7 Explain why the mass of the egg changed in this way.

8 What do you think about eggs like this as a model for showing osmosis in animal cells?

9 Are there any problems with this as a model for animal cells?

ANSWERS1 The shell of the egg is removed to reveal the egg membrane. The shell

is rigid and will not change in shape or size. Without the shell the membrane can expand or contract.

2 You dry the eggs with a paper towel to make sure that the change in mass is due to the fluid inside the egg membrane, not to drops of water on the outside.

3 Comparing the percentage change in mass takes account of differences in the size of the eggs. A small egg could increase by a smaller amount than a large egg, but it could be a larger percentage increase.

4 The egg in 20% sodium chloride has lost mass.

5 This is because the concentration of solutes inside the egg membrane is less than 20% sodium chloride, so water has diffused out through the selectively permeable egg membrane. This is osmosis.

6 The egg in 0% sodium chloride has gained mass.

7 This is because the concentration of solutes inside the egg membrane is more than that of 0% sodium chloride, so water has diffused in through the selectively permeable egg membrane. This is osmosis.

8 These eggs are a nice big, easy to handle example of animal tissue which makes it easy to see what is going on.

9 A chicken’s egg is not a single cell, and the egg membrane is a different structure from a cell membrane although it shares some of its properties.