Biology A-Level Bridging Work – Summer 2020

What does this course require of me? Biology at A-level is the study of all forms of life, in particular animal, plant and bacterial. We range freely from sub-cellular structures and reactions all the way up to looking at how whole ecosystems of organisms interact with each other and with the environment. You’ll require good critical thinking skills and an ability to persevere in order to see the bigger picture of how small structural components work together to solve physiological or ecological challenges. The course requires a lot of very hard work – our syllabus is the biggest in terms of the volume of things there are to learn and whilst we ensure that we make it accessible for you, there is so much to remember that you will need to commit to working and learning the detail from the very first lessons. If you’re the kind of student who relies on last-minute revision, you are not likely to achieve well on the course. Good English language skills are important as you’ll find quickly that knowing the facts is only the building blocks – you only start to really achieve the highest grades when you are able to accurately synthesise large answers from the individual pieces of knowledge you have in your head. Finally, you will need to be a competent mathematician. A-level Biology involves much more maths than you will have been used to at GCSE and there are a minimum number of marks on each paper that are awarded for mathematical questions. You will also need to be prepared to learn three different statistical tests and be able to apply them in new situations. How will this unit help me to prepare for the A level? The topics and skills covered in this unit will prepare you for the first few weeks of the course. It will help you to extend your knowledge of three of the fundamental components of the course – Cell Biology, Enzymes and Nucleic Acids – from what you have learned at GCSE to the level expected of a Year 12 student. In addition, we’ve highlighted two mathematical techniques that Year 12 students need to see as being ‘easy’ by the time we’ve covered them that link directly to things with which you should already be familiar. The example questions on Magnification calculations and Percentage Change will mean that you can be confident you have these skills ready for the start of the course. All of the tasks in this booklet are supported by the CGP ‘Head Start to A-level Biology’, which is available for free at https://www.amazon.co.uk/Head-Start-level-Biology-Level/dp/1782942793.

Biology A Level – Bridging Work

Cells - What can you remember from GCSE?

• As microscopes technology improved it became possible to magnify and resolve images to a higher standard.

• This allowed a more detailed structure of cells. • It revealed many more organelles. • An organelle is a structure within a cell which carries out a function.

This is the structure of an animal cell in the detail required for A level. It obviously shows considerably more detail and by the time you’ve finished this unit of work you’ll be much more familiar with it and with the reactions which happen inside it.

What is the difference between magnification and resolution?

Biology A Level – Bridging Work

Task 1: Comparing animal, plant and prokaryotic cells. 1) Fill in the gaps

It was once common practice to classify all living organisms as either animals or plants. With improved knowledge of living things it has become apparent that there are ______ fundamentally different types of cell. The most obvious difference between the two types is that one possesses a nucleus and the other does not.

The cells of animals, ___________ and fungi contain many organelles some of which are bound by a membrane. These are referred to as ______________ cells. The cells of bacteria are very different, they lack membrane bound organelles such as a _____________. This type of cell is referred to as a _______________ cell (meaning before nucleus). Prokaryotic cells are about 1000 to 10000 times smaller than eukaryotic cells and are much simpler in structure. Biologists believe eukaryotes evolved from ________________.

2) Eukaryotic cells contain membrane-bound organelles, give 3 examples:

3) Prokaryotic cells have one membrane, where is it?

Biology A Level – Bridging Work

4) Use table 1 to compare plant (eukaryote), animal (eukaryote) and prokaryotic cells. For each cell type indicate whether the feature is present or absent using a tick or cross.

Feature Plant cells Animal cells Prokaryote cells

Chloroplasts

Large permanent vacuole

Cellulose cell wall

Peptidoglycan (murein) cell wall

Linear chromosome

Circular chromosome

Plasmids

Endoplastic Reticulum

Golgi body

DNA free in the cytoplasm

ATP is produced in the

mitochondria ATP is produced at infolded

regions of the cell membrane

called mesosomes

Ribosomes

Cell membrane

DNA organised in chromosomes in the

nucleus

5) Give 2 ways in which prokaryotes are useful to humans

6) Mitochondria and chloroplasts contain small loops of DNA similar to the plasmids found

in prokaryotic cells. These organelles also contain ribosomes that are the same size as prokaryotic ribosomes. Can you suggest an explanation for these features?

Biology A Level – Bridging Work

Task 2: Find the role of each of the highlighted organelles and link their structure to their function.

You may find it helpful to construct a table on a piece of ‘landscape’ A4 paper like the following to lay out your research. Each box will contain a small paragraph rather than a few words.

Organelle Structure Function How does its

structure help it carry out its

function?

Lysosome

Eg 2….

Biology A Level – Bridging Work

Task 2: Use your knowledge of GCSE magnification calculations to work out the following:

Using the formula: Image Size = Actual Size x Magnification,

Calculate the magnification of the cell

Calculate the length of structure G, a mitochondrion.

Calculate the diameter of the nucleolus

Calculate the diameter of the nucleus

Calculate the diameter of the cell at its widest point.

Biology A Level – Bridging Work

Task 3: DNA structure vs RNA structure

Draw and describe the structure of DNA.

Include the key words:

phosphate, sugar, backbone, pentose, carbon, nitrogen containing bases, adenine,

guanine, cytosine, thymine, polymer, nucleotide, deoxyribose, phosphodiester

bond, double helix, hydrogen bonding, complementary base pairs, genetic code.

Draw and describe the structures of mRNA, tRNA and rRNA. Include the following key words:

polymer, nucleotides, uracil, guanine, cytosine, adenine, mRNA, tRNA, rRNA.

Use what you’ve found to compare and contrast DNA with RNA. ‘Comparisons’ are features of the two which are the same. ‘Contrasts’ are features of the two which are different. e.g. DNA and RNA both contain nucleotides. DNA contains Adenine, Cytosine, Guanine and Thymine RNA contains Adenine, Cytosine, Guanine and Uracil. Aim for 5 comparisons and 3 contrasts.

Biology A Level – Bridging Work

Task 4: Enzyme Reactions

Draw annotated diagrams to explain the following:

Lock and key theory.

Induced fit theory.

How enzymes lower activation energy.

How enzyme- substrate complexes form. Each of these bullet points represents a key theme of the topic of ‘enzymes’ and you should create a diagram and paragraph which clearly represent each one.

Task 5: Enzyme Reaction Rates

Draw annotated diagrams to explain the following:

How the rate of a reaction is affected by: o enzyme concentration, o substrate concentration, o pH o temperature.

What are competitive inhibitors?

What are non-competitive inhibitors? Each of these bullet points represents a key theme of the topic of ‘enzymes’ and you should create a diagram and paragraph which clearly represent each one.

Biology A Level – Bridging Work

Task 6: Calculating Percentage Change Calculating percentage change is a fundamental skill in Biology. It appears in some format on every set of exam papers, usually more than once. e.g. If a potato stick begins an osmosis experiment with a length of 50mm and expands to 55mm, what is its percentage change in length? Percentage change = Change x 100 Original In this case, our ‘change’ is the change in length. Our ‘original’ is the original length. So: Percntage Change = 5 x 100 50 = 10% Calculate the percentage changes for these situations: 1. A potato tube starts at a length of 50mm and expands to 60mm. 2. A potato tube starts at a length of 50mm and expands to 70mm. 3. A potato tube starts at a length of 50mm and shrinks to 40mm. 4. A potato tube starts at a length of 45mm and shrinks to 30mm. 5. There are 17000 animals in a population in 2016 and 210,000 in 2018. What is the percentage increase? 6. If the height of a tree rises from 1.8m to 2.3m in ten years, what is the percentage increase per year? 7. In a decade, the number of trees in a forest falls from 10,000 to 4,700. What is the percentage decrease? 8. If a baby increases in mass by 1.2kg in a week, what is the percentage increase per day?

Biology A Level – Bridging Work

Task 7: Comprehension of Scientific Literature Read the Chapter “The Stuff of Life” from ‘A Short History of Nearly Everything’ by Bill Bryson which is attached to this document. When you have read through it carefully, answer the following questions.

The Stuff of Life – DNA 1. Explain how it is true to say that most people of the same ethnic background are closely related. 2. Calculate the number of ancestors you have if you go back 30 generations. 3. How many yards of DNA are there in your body? 4. How does RNA ‘get messages to proteins’? 5. Why are fruit flies a good species to use for genetics trials? 6. Why would Avery’s 1944 experiment be ethically unsound? 7. Why do many people feel Franklin was wrongly overlooked for a Nobel prize? 8. What are the strengths and weaknesses of saying that DNA is ‘like a ladder’? 9. Research and outline the technique behind X-Ray crystallography and what it has been used to discover in Biology.