☀️GCSE Biology Edexcel IGCSE☀️Higher☀️- Topic 2: Structure and Functions in Living Organisms Notes☀️
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Science
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GCSE
Complete set of notes for each specification point (2.1 - 2.95) for Topic 2 (Structure and Functions in Living Organisms) of the GCSE Biology Edexcel IGCSE Exam Board. Suitable for 2024 or 2025 exams. Written by a GCSE Student, using lots of resources to create accurate notes to aid exams. Includes...
2. STRUCTURE AND FUNCTIONS IN LIVING ORGANISMS
A – Level of organisations:
2.1 – describe the levels of organisations in organisms: organelles, cells, tissues, organs and systems
o Organelles – a component within a cell that carries out a specific task
o Cells – basic functional and structural building blocks of all living organisms
o Tissues – a group of cells of similar structure working together to perform a specific function
o Organs – made from a group of different tissues working together to perform a specific function
o Organ in plants: leaf, shoots, roots
o Organ system – made from a group of organs with related functions, working together to perform specific
functions within the organisms
o Systems in body: circulation, nervous (CNS), respiratory, digestive, urinary, skeletal, endocrine
(hormonal), reproductive, immune, lymphatic
B – Cell structure:
2.2 and 2.3 – describe cell structures and functions of: the nucleus, cytoplasm, cell membrane, cell wall,
mitochondria, chloroplasts, ribosomes and vacuole
Found in plant and animal cells:
o Nucleus – contains the genetic material in chromosomes which controls how cells grow and work
o Cytoplasm – jelly liquid substance, where chemical reactions occur, organelles are found in it
o Cell membrane – holds the cell together, controls the substances entering and leaving the cell
o Mitochondria – the site of aerobic respiration, provides energy for the cell
o Ribosomes – site of protein production in protein synthesis
Found only in plants:
o Chloroplasts – contains green chlorophyll pigments (to absorb light energy) needed for photosynthesis, where
photosynthesis takes place – provides food for the plant
o Permanent vacuole – contains cell sap, used for storage of materials, helps support the shape of the cell
o Cell wall – made of cellulose, gives the cell extra support, defines the cell’s shape
2.4 – know the similarities and differences in the structure of plant and animal cells
2.5 – explain
the
importance of cell differentiation in the development of
specialised cells
o Specialised cells – cells which have certain characteristics to perform particular functions
Specialised cells in animals: mucus, sweep hair, dust and bacteria from throat)
o Red blood cell (for transport of oxygen) – biconcave disc Specialised cells in plants:
shape (more surface area for more efficient diffusion),
o Root hair cell (uptake water and soil from soil) –
no nucleus (more amount of space for haemoglobin),
root hair (big surface area), thin walls (water moves
haemoglobin (for transportation)
quickly)
o Ciliated cell (movement of mucus) – cilia (hair-like
structures extending from cytoplasm to move
, 2. STRUCTURE AND FUNCTIONS IN LIVING ORGANISMS
o Palisade leaf cell (enable photosynthesis) – packed
with chloroplasts, column shaped (maximise
sunlight)
2.6 – understand the advantages and disadvantages of using stem cells in medicine
o Stem cells – undifferentiated cell which can undergo division to produce many more similar cells
o Important for growth and repair and development
Example – embryonic stem cells:
o Form when an egg and sperm cell fuse to form a zygote
o They can differentiate into any type of cell in the body
o Scientists can clone these cells
o Found in early human embryos
Advantages Disadvantages
Can be used to replace damaged cells, such as type 1 diabetes Ethical issues of destroying unused embryos
Bone marrow transplants for adult stem cells can be used to treat No guarantee in how successful these therapies
cancers, such as leukaemia will be an if there will be any long term effects
Can grow whole organs for transplants Mutations could occur in cultured stem cells
No rejection, if it is made from the patient’s own cells Difficult to find suitable stem cell donors
Can allow for testing potential drugs without animal testing
C – Biological molecules:
2.7 – identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)
o Carbohydrates – carbon, oxygen and hydrogen
o Proteins – carbon, oxygen, hydrogen, nitrogen, sulphur and phosphorus
o Lipids – carbon, oxygen and hydrogen
2.8 – describe the structure of carbohydrates proteins and lipids are large molecules made from smaller basic
units
Carbohydrates:
o Made of simple sugars – e.g. maltose and glucose
o Starch and glycogen (large complex carbohydrates) are
made from simple sugars
o Long chain of starch = polymer
o Glucose = monomer
Proteins:
o Formed from long chains of 20 different amino acids
o Amino acids can be arranged in any order there are
hundreds of thousands of different proteins
o Long chain of protein = polymer
o Amino acids = monomer
Lipids:
o Made up of fat molecules
o Fat molecules are made up of one glycerol molecules
chemically bonded to three fatty acids
, 2. STRUCTURE AND FUNCTIONS IN LIVING ORGANISMS
o Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)
2.9 – practical: investigate food samples for the presence of glucose, starch, protein and fat
2.10 – understand the role of enzymes as biological catalyses in metabolic reactions
o Enzymes – proteins that act as biological catalysts to speed up the rate of a chemical reaction without being
changed or used up in the reaction
o They are biological because they are made in living cells
o Enzymes = necessary to all living organisms they maintain reaction speeds of all metabolic reactions (all
the chemical reactions that happen in a cell of organis to keep it alive) at a rate that can sustain life
o For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one
meal; with enzymes, it takes around 4 hours
Extra:
o Enzymes are very specific
o The active site of an enzyme, where the substrate attaches, is a
complementary shape to the substrate (‘lock and key’ model)
o A substrate enters the active site of the enzyme. This forms the
enzyme-substrate complex. The reaction then occurs, converting the
substrate into products and forming an enzyme products complex.
o All enzymes can not change shape (unless denatured) so they can work again and again
2.11 – understand how temperature changes can affect enzyme function, including changes to the shape of
active site
o As the temperature increases, moleculues move more quicky and collide more often – the reaction rate increases
o If it gets too hot, some of the bonds holding the enzyme together break
o Once the temperature goes over 40 degrees, the enzyme becomes denatured and the active site changes shape,
so the substrate can no longer bind with it (irreversible process)
o Optimum temp = where the enzyme is most active = 37 – 40 degrees (37.5 degrees)
2.12 – practical: investigate how enzyme activity can be affect by changes in temperature
2.13 – understand how enzyme function can be affect by changes in pH altering the active site
o If pH is too high or too low, the pH interferes with the bonds holding the enzyme together
o The active site changes and the enzyme is denatured
o Optimum pH = often neutral pH 7 (but not always)
2.14 – practical: investigate how enzyme activity can be affected by changes in pH
D – Movement of substances into and out of cells:
2.15 – understand the processes of diffusion, osmosis and active transport by which substance move into and
out of cells
Diffusion:
o Movement of molecules from an area of higher concentration to an area of lower concentration
o Water moves down its concentration gradient
o Passive process which doesn’t require energy
o Happens in both liquids and gases free to move about randomly
, 2. STRUCTURE AND FUNCTIONS IN LIVING ORGANISMS
o The bigger the difference in concentration, the faster the diffusion rate
o EXAMPLES: small intestine, moving digested food products from the lumen of the small intestine to the blood OR
leaves moving oxygen between air spaces to mitochondria in all cells
Osmosis:
o Net movement of water molecules from an area of higher water potential (dilute solution) to an area of lower
water potential (concentrated solution) across a partially permeable cell membrane
o Water moves down its concentration gradient
o The cell membrane is partially permeable allows small molecules (like water) through but not larger molecules
(like solute molecules)
Hypertonic (lower water potential than the cell):
In plant cells: o Loses water by osmosis
o Less water than normal
o More water goes out that what comes in
o Vacuole gets smaller, cell membrane shrivels
away from the cell wall
Hypotonic (higher water potential than the cell):
o Gains water by osmosis
o More water than normal
o More water going in, than coming out
Flaccid Normal Turgid
o Vacuole gets bigger, cell membrane pushes
against the cell wall
Active transport:
o Movement of particles from an area of lower concentration to an area of higher concentration using energy
released during respiration
o Energy is needed because particles are being moved against a concentration gradient
o EXAMPLES: plants get minerals from the soil (low mineral conc.) to their root hair cells (high mineral conc.)
2.16 – understand how factors affect the rate of movement of substances into and out of the cells, including
the effects of surface area to volume ratio, distance, temperature and concentration gradient
1. Surface Area to Volume Ratio:
o The bigger a cell or structure is, the smaller the surface area to volume ratio
o Many cells are adapted for diffusion by increased surface area – e.g. root hair cells in plants
o Calculating: ratio between surface area (add the area of all sides) and the volume (l × w × h)
2. Distance:
o The smaller the distance the molecules have to travel, the faster the transport will occur
o Blood capillaries and alveoli have walls which are one cell thick to ensure the diffusion rate is as fast as possible
3. Temperature:
o The higher the temperature, the more kinetic energy, the faster molecules move
o This results in more collisions against the cell membrane and a faster rate of diffusion occurs
4. Concentration Gradient:
o The greater the difference in concentration on either side of the membrane, the faster diffusion rate
o This only increases the rate of diffusion and osmosis, NOT active transport
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