Unit 1 notes for IB Biology HL students. I took my exams in July 2022 and got a 7 in Biology HL. The notes are a combination of information from different sources with a main focus on the IB Biology Textbook.
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1.1 Introduction to Cells
Objectives:
❏ Understanding:
❏ According to the cell theory, living organisms are composed of cells
❏ Organisms consisting of only one cell carry out all functions of life in that cell
❏ Surface area to volume ratio is important in the limitation of cell size
❏ Multicellular organisms have properties that emerge from the interaction of their cellular
components
❏ Specialised tissues can develop by cell differentiation in multicellular organisms
❏ Differentiation involves the expression of some genes and not others in a cell’s genome
❏ The capacity of stem cells to divide and differentiate along different pathways is necessary for
embryonic development. It also makes stem cells suitable for therapeutic uses
❏ To be able to:
❏ Question the cell theory using atypical examples, including striated muscle, giant algae and
aseptate fungal hyphae
❏ Investigate the functions of life in Paramecium and one named photosynthetic unicellular
organism
❏ Use of stem cells to treat Stargardt’s disease and one other named condition
❏ Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical
cord blood of a new-born baby and from an adult’s own tissues
❏ Skills
❏ Use of a light microscope to investigate the structure of cells and tissues
❏ Draw cell structures as seen with the light microscope
❏ Calculation of the magnification of drawings and the actual size of structures shown in
drawings or micrographs
❏ Nature of Science
❏ Looking for trends and discrepancies: although most organisms conform to cell theory, there are
exceptions
❏ Ethical implications of research: research involving stem cells is growing in importance and
raises ethical issues
The Cell Theory:
- The cell theory states that:
1. Cells are the fundamental building blocks of all living organisms (i.e. all living organisms are
composed of cells)
- Unicellular organisms are composed of one single cell (e.g. bacteria) and therefore are
the smallest type of organisms possible.
- Multicellular organisms (e.g. humans) are composed of many cells
2. The cell is the smallest unit of life and they are the smallest structures capable of surviving on
their own
3. Cells arise from pre-existing cells (e.g. new cells arise from cell division and a zygote (the very
first cell formed when an organism is produced) arises from the fusion of an egg cell and a sperm
cell)
- The internal structure of living organisms is built up from very small individual parts
- Although there was much variation, certain features were seen again and again. A theory was developed to
explain the basic features of structure - the cell theory
- Cells vary considerably in size and shape but they share certain common features:
1. Every living cell is surrounded by a membrane, which separates the cell contents from everything
else outside
2. Cells contain genetic material which stores all of the instructions needed for the cell’s activities
, 3. Many of these activities are chemical reactions, catalysed by enzymes produced inside the cell
4. Cells have their own energy release system that powers all of the cell’s activities
The Seven Functions of Life (MR GREHN):
- The function of life are things that all organisms must do to stay alive
1. Metabolism - chemical reactions inside the cells, including cell respiration to release energy
2. Response - the ability to react to changes in the environment
3. Growth - A permanent increase in size and dry mass by an increase in cell number or cell size or both
4. Reproduction - producing offspring either sexually or asexually
5. Excretion - getting rid of the waste products of the metabolism
6. Homeostasis - A tendency to maintain a balanced or constant internal state; the regulation of any aspect of
body chemistry, such as blood glucose, around a particular level
7. Nutrition - the process of providing or obtaining the food necessary for health and growth.
What is the unit of life? The boy or his cells?
- The boy = holistic approach
- His cells = reductionist approach
Using Light Microscopes:
Use of a light microscope to investigate the structure of cells
and tissues
1. Learn the names and parts of the microscope
2. Understand how to focus the microscope to get the
best possible image
3. Look after your microscope so it stays in perfect
working order
4. Know how to troubleshoot problems
- Focusing
1. Put the slide on the stage with the most
promising region exactly in the middle of the
hole in the stage that light comes through
2. Always focus at low power first even if
eventually you need high power
magnification
3. Focus with the larger coarse-focusing knobs first, then when you have nearly got the image in
focus make it really sharp using the smaller fin-focusing knobs
4. If you want to increase the magnification, move the slide so the most promising region is exactly
in the middle of the field of view and then change to a higher magnification lens
- Looking after a microscope
1. Always focus by moving the lens and the specimen further apart, never closer to each other
2. Make sure that the slide is clean and dry before putting it on the stage
3. Never touch the surfaces of the lenses with your fingers or anything else
4. Carry the microscope carefully with a hand under it to support its weight securely
- Troubleshooting
1. Problem: Nothing is visible when I try to focus
a. Solution: Make sure the specimen is actually under the lens, by carefully positioning the
slide (it is easier to find the specimen if you focus at low power first
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