B1 - Characteristics of living organisms

Movement: an action by an organism or part of an organism causing a change of position or place

Respiration: the chemical reactions in cells that break down nutrient molecules and release energy for
metabolism
Sensitivity: the ability to detect and respond to changes in the internal or external environment
Growth: a permanent increase in size and dry mass
Reproduction: the processes that make more of the same kind of organism
Excretion: the removal of waste products of metabolism and substances in excess of requirements
Nutrition as the taking in of materials for energy, growth and development

NOT A CHARACTERISTIC
Metabolism: all chemical processes that occur in your body to keep it running

B2 - Cells
B2.1 Cell structure:
Plant and animal cells:
Cell Wall (PLANTS ONLY)
-​ A rigid outer layer made of cellulose that supports and protects plant cells.
-​ Found only in plant cells.
-​ Made of cellulose.

Cell Membrane
-​ A partially permeable membrane that controls the movement of substances into and out of the
cell.
-​ Found in both plant and animal cells.

Nucleus
-​ Contains genetic material (DNA) and controls cell activities such as growth and reproduction.

Cytoplasm
-​ A jelly-like substance where chemical reactions take place.
-​ It contains organelles like mitochondria and ribosomes.

Chloroplasts (PLANTS ONLY)

-​ Contain chlorophyll, which absorbs light energy for photosynthesis.
-​ Found only in plant cells.

Ribosomes
-​ Tiny structures that synthesize (make) proteins by joining amino acids together.

Mitochondria
-​ The site of aerobic respiration, where energy is released from glucose in the form of ATP.

Vacuoles (PLANTS ONLY- BIG VACOULES)

 -​ Plant cells: Contain a large central vacuole filled with cell sap to maintain shape and store
substances.

-​ Animal cells: May have small vacuoles.

Rough Endoplasmic Reticulum (RER) is a network of membranes with ribosomes on its surface that
helps transport proteins made by ribosomes.​

Ribosomes are small structures that synthesize proteins and can be found either free in the cytoplasm or
attached to the RER.(usually shown as dots)

Compare the structure of a plant cell with an animal cell:

1. Chloroplasts

●​ Function: Carry out photosynthesis—converting light energy into glucose using carbon dioxide
and water.
●​ Why unique to plant cells: Animals do not photosynthesize, so they don't need chloroplasts.
Plants make their own food, while animals eat other organisms.

2. Cell Wall

●​ Function: Provides rigid structure, protection, and support. Made of cellulose.

●​ Why unique to plant cells: Animals have flexible cell membranes to allow movement. Plants
need firm structure to stand upright and resist external forces(gravity, wind, water).​

3. Large Central Vacuole

 ●​ Function: Stores water, nutrients, and waste; helps maintain turgor pressure (keeps the plant
firm).
●​ Why unique to plant cells: While animal cells have small vacuoles, plant cells have one large
central vacuole to maintain structure and store more substances.

Bacteria cell

Cell wall:
●​ Made of peptidoglycan
●​ Provides structure and protection

Cell membrane:
●​ Controls what enters and leaves the cell

Cytoplasm:
●​ Site of chemical reactions
●​ Contains enzymes and ribosomes​

Ribosomes:
●​ Make proteins
●​ Smaller than those in plant and animal cells

Circular DNA:
●​ Single loop of genetic material
●​ Controls cell functions
●​ Not enclosed in a nucleus

Plasmids:
●​ Small, extra loops of DNA
●​ May carry genes for antibiotic resistance or other useful traits
Flagellum (in some bacteria):
●​ Long tail-like structure
●​ Used for movement (helps the cell swim)​

Types of cells:

Prokaryotic cells

●​ Meaning: Simple cells without a nucleus or membrane-bound organelles.

●​ Examples: Bacteria and Archaea.

Eukaryotic cells

●​ Meaning: Complex cells that have a nucleus and membrane-bound organelles.

●​ Examples: Plant, animal, fungal, and protist cells.

The main differences between prokaryotic and eukaryotic cells

Feature Prokaryotic Cells Eukaryotic Cells

Nucleus ❌ No true nucleus (DNA is free in ✅ Has a true nucleus with a nuclear
cytoplasm) membrane

Cell Wall ✅ Present (but not made of

cellulose)
✅ In plant cells (made of cellulose)

Membrane-bound
organelles
❌ Absent ✅ Present (e.g., mitochondria,
chloroplasts)

Size Smaller (1–10 µm) Larger (10–100 µm)

DNA form Circular DNA (single loop) Linear chromosomes in nucleus

Ribosomes Smaller (70S) Larger (80S)

 Examples Bacteria, Archaea Animals, plants, fungi, protists

Membrane-bound organelles – Meaning:

●​ Organelles that are surrounded by a membrane (like a skin) inside a eukaryotic cell.
●​ These membranes separate the organelle’s contents from the rest of the cell, allowing them to do
special jobs.
●​ e.g Nucleus , Mitochondria , Chloroplasts, Endoplasmic reticulum

How are new cells produced?

●​ New cells are produced by division of existing cells

State that specialised cells have specific functions, limited to:

(a). ciliated cells – movement of mucus in the trachea and bronchi

(b). root hair cells – absorption (lots of surface area for diffusion & osmosis)
(c). palisade mesophyll cells – photosynthesis(lots of chlo
(d). neurones – conduction of electrical impulses
(e). red blood cells – transport of oxygen(concave shape)
(f). sperm and egg cells (gametes) – reproduction

The hierarchy of biological organization

PROGRESSION—from cell → tissue → organ → organ system → organism

1. Cell

●​ Definition: The smallest unit capable of carrying out all life processes.​

●​ Example:​

○​ Red blood cell – transports oxygen​

○​ Neurone – conducts electrical impulses

2. Tissue

●​ Definition: A group of similar cells working together to perform a specific function.​

●​ Example:​
 ○​ Palisade mesophyll tissue in plant leaves – specialized for photosynthesis​

○​ Ciliated epithelium in human airways – moves mucus ​

3. Organ

●​ Definition: A structure composed of two or more different types of tissues collaborating to carry
out one or more functions.​

●​ Example:​

○​ Leaf – contains photosynthetic tissue, vascular tissue (xylem & phloem), guard cells, etc.​

○​ Heart – muscle tissue, valves, blood vessels for pumping blood

4. Organ System

●​ Definition: A collection of organs that together perform a major bodily function.​

●​ Example:​

○​ Digestive system – mouth, oesophagus, stomach, intestines, liver, pancreas, etc.​

○​ Circulatory system – heart, arteries, veins, capillaries

5. Organism

●​ Definition: A complete, living entity capable of independent existence; made up of organ systems
functioning together.​

●​ Example:​

○​ Human – multiple organ systems (nervous, circulatory, digestive…)​

○​ Plant – roots, stem, leaves, reproductive structures working as a whole organism​

B2.2 Size of specimens:

 ●​ Calculate magnification and size of biological specimens using millimetres as units

●​ Convert measurements between millimetres (mm) and micrometres (μm)

1𝑚𝑚 = 1000 𝑢𝑚

B3 - Movement into and out of cells

B3.1 Diffusion
Diffusion: the net movement of particles from a region of their higher concentration to a region of their
lower concentration (i.e. down a concentration gradient), as a result of their random movement
○​ Some substances move into and out of cells by diffusion through the cell membrane

Describe the importance of diffusion of gases and solutes in living organisms(WHERE

DOES DIFFUSION OCCUR)

Diffusion is essential because it allows the movement of substances from an area of high
concentration to an area of low concentration, which is vital for life processes. Some key
examples include:

●​ Gas exchange: Oxygen diffuses from the air in the alveoli into the blood, and carbon
dioxide diffuses from the blood into the alveoli to be exhaled.​

●​ In plants: Carbon dioxide diffuses into leaves for photosynthesis, and oxygen diffuses
out as a by-product.​

●​ Nutrient absorption: In the small intestine, digested nutrients (like glucose and amino
acids) diffuse into the bloodstream.​

●​ Waste removal: Waste substances (e.g., urea) diffuse from cells into the blood for
excretion by the kidneys.

Investigate the factors that influence diffusion, limited to: surface area, temperature,
concentration gradient and distance

1. Surface Area

●​ The larger the surface area, the more space there is for particles to cross the membrane at the
same time. This increases the rate of diffusion because more particles can move through in a
given time.
○​ Structures in organisms are often adapted to maximize surface area.
○​ Example: The alveoli in the lungs and villi in the small intestine have large surfaces to
increase surface area, speeding up gas and nutrient exchange.
2. Temperature

●​ Increasing temperature gives particles more kinetic (movement) energy, so they move faster.
Faster particles collide more often and spread out more quickly, increasing the diffusion rate.
○​ In warm-blooded animals, maintaining a high internal temperature helps to keep diffusion
(like gas exchange and enzyme reactions) working efficiently. Too high a temperature,
though, can damage cells or denature proteins

3. Concentration Gradient

●​ How it affects diffusion:​

A concentration gradient is a measure of the difference in concentration of a certain particle
between two different areas. The steeper the concentration gradient, the greater the difference in
concentrations. This means, more particles will move from their region of higher concentration to
their region of lower concentration to achieve equilibrium, thereby increasing the rate of
diffusion.
○​ Cells often maintain steep concentration gradients to keep diffusion efficient.​
Example: Oxygen levels are high in alveoli and low in blood, so oxygen diffuses quickly
into the bloodstream.

4. Distance

●​ How it affects diffusion:​

The shorter the distance particles have to travel, the faster diffusion occurs. Over long
distances, diffusion becomes slow and inefficient.​

○​ Many exchange surfaces (like capillary walls, alveoli, and cell membranes) are one cell
thick to minimize diffusion distance and allow rapid movement of substances.​
If tissues swell or get damaged, increasing the distance, diffusion becomes slower, which
can affect function.

B3.2 Osmosis
Osmosis: the net movement of water molecules from a region of higher water potential (dilute solution)
to a region of lower water potential (concentrated solution), through a partially permeable membrane
○​ Water diffuses through partially permeable membranes by osmosis
○​ Some substances move into and out of cells by diffusion through the cell membrane

Investigate and describe the effects on plant tissues of immersing them in solutions of different
concentrations AND Explain the effects on plant tissues of immersing them in solutions of different
concentrations by using the terms turgid, turgor pressure, plasmolysis and flaccid.

Things you will need to know before we start:

●​ Plant cells have cell walls – this is quite important when thinking about the effect of immersing
plant tissue in solutions of different concentrations.
●​ Cells are primarily made of water (on average, about 70% of total cell mass is water).
●​ Every cell cytoplasm has its own specific concentration of solutes, and this concentration is
usually pretty similar across the same type of tissue (e.g. palisade cells will have similar
 concentrations of solutes in their cell cytoplasms), and that the pressure that water applies in
plants (i.e. the water pressure), is known as turgor pressure.
○​ Turgidity is the state of being ‘turgid’ or swollen, especially due to high fluid content.
○​ Plants need turgid cells to help them maintain their shape and in turn, help the plant stay
upright.
○​ Water is mainly stored in the vacuole in the cytoplasm, and it is mainly this vacuole that
regulates the turgidity of a plant cell.

Now, let’s move on to the main matter of this learning objective:

●​ When you immerse plant tissue in solutions of lower water potential (hypertonic solution) than
that of the plant cells:
○​ Water diffuses out of the cell by osmosis. This means there is less matter inside the cell.
○​ This causes the cytoplasm to shrink, and thus the cell membrane gets ripped away from
the cell wall. This process is called plasmolysis. Cells become weak and flaccid, as there
isn’t enough cytoplasm to support the cell and help it maintain its shape.
○​
●​ When you immerse plant tissue in a solution of equal water potential to their cell cytoplasm
(isotonic solution).
○​ Since the concentration of the solution is equal inside and outside of the plant cells, there
is no net movement of water. This means the volume or shape of the plant cell is
unlikely to change.
●​ When you immerse plant tissue in solutions of higher water potential than their cell cytoplasm
(hypotonic solution).
○​ Here, the solution inside the cells is more concentrated than solution outside, so water
diffuses down its concentration gradient into the cell, by osmosis. This causes the amount
of cell matter inside the cell to increase. As the cytoplasm enlarges, it pushes outwards on
the cell surface membrane more and more. Normally, this would usually cause the cell
surface membrane to eventually burst (once the pressure, otherwise known as turgor
pressure, in this case, grows too large). However, plant cells have very strong cell walls.
This holds the plant cell intact, and as the cytoplasm pushes outside, the cell simply
swells to its full size and becomes rigid. This cell is turgid.
KEY DEFINITIONS:

★​ A solute is the substance that is dissolved, and a solvent is the substance that does the dissolving.
Together, the solute and solvent form a solution. For example, in salt water(solution), salt is the
solute and water is the solvent.

Hypertonic solution: A solution with lower water potential (i.e., more solute - less water)) than the
cell's cytoplasm.

●​ Water moves out of the cell by osmosis.

Hypotonic solution: A solution with higher water potential (i.e., less solute - more water) than the
cell's cytoplasm.

●​ Water moves into the cell by osmosis.

Isotonic solution: A solution with the same water potential as the cell’s cytoplasm.

●​ There is no net movement of water.

Plasmolysis: The process in which the cell membrane pulls away from the cell wall due to water loss by
osmosis in a hypertonic solution.

Plasmolyzed/SHRINKED (cell): A shrunken plant cell that has undergone plasmolysis — the cytoplasm
has shrunk and detached from the cell wall. HYPERTONIC SOLUTION

Flaccid: A plant cell that has lost some water and is soft/weak, but the cell membrane has not fully pulled
away from the cell wall. ISOTONIC SOLUTION

Turgid: A swollen and firm plant cell that has taken in water and is pressing tightly against the cell wall
due to turgor pressure. This keeps plants upright. HYPOTONIC SOLUTION

Explain the importance of water potential and osmosis in the uptake of water by plants

In Plants:

●​ Water Uptake: Water moves by osmosis from the soil (higher water potential) into root hair cells
(lower water potential) to keep the plant hydrated.​
 ●​ Turgor Pressure: Water entering plant cells makes them turgid, helping the plant stay firm and
upright.​

●​ Water Loss: If water potential outside the cell is lower (e.g., dry soil), water leaves the cells by
osmosis, making them flaccid and causing the plant to wilt.​

In Animals:

●​ Cell Hydration: Osmosis maintains water balance in animal cells.​

○​ In a hypotonic solution (higher water potential outside), water enters the cell, which may
swell and burst (lysis).​

○​ In a hypertonic solution (lower water potential outside), water leaves the cell, causing it
to shrink (crenation).​

●​ Water Regulation: Animals rely on osmosis and water potential differences to absorb water,
remove excess, and maintain stable internal conditions through processes like sweating, drinking,
and excretion.

B3.3 Active transport

Active transport: the movement of particles through a cell membrane from a region of lower
concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from
respiration

Explain the importance of active transport as a process for movement of molecules or ions across
membranes, including ion uptake by root hairs

Importance of Active Transport:

●​ Allows absorption of essential substances that are in lower concentration outside the cell than
inside.

●​ Maintains concentration gradients that are crucial for processes like nerve impulse
transmission and muscle contraction.

●​ Enables cells to accumulate nutrients and ions they need, even when these are scarce in the
environment.

Example: Ion Uptake by Root Hair Cells in Plants

●​ Root hair cells absorb mineral ions (like nitrates, potassium, magnesium) from the soil.
 ●​ These minerals are often in very low concentrations in the soil compared to inside the root cell.
●​ To take in these ions against the concentration gradient, the root hair cells use active
transport.
●​ This is essential for plant growth, as these minerals are required for:​
​ - Making proteins (nitrates)​
​ - Photosynthesis (magnesium for chlorophyll)​
​ - Enzyme function (potassium)

B4 - Biological Molecules
List the chemical elements that make up:
●​ Carbohydrates: carbon, hydrogen, oxygen
●​ Fats: carbon, hydrogen, oxygen(little)
●​ Proteins: nitrogen, carbon, hydrogen, oxygen

State that large molecules are made from smaller molecules, limited to:
(a). starch, glycogen and cellulose from glucose
(b). proteins from amino acids
(c). fats and oils from fatty acids and glycerol

Describe the use of:

(a). iodine solution test for starch
●​ Solution: Iodine
●​ Positive: Blue - Black
●​ Negative: Yellow
(b). Benedict’s solution test for reducing sugars - HOT WATER BATH
●​ Solution: Benedict solution
●​ Positive: Brick red(orange, yellow or green if less sugar is present)
●​ Negative: Blue

(c). biuret test for proteins

●​ Solution: Biuret solution // if not mixed→sodium hydroxide AND copper sulphate
●​ Positive: Purple
●​ Negative: Blue
(d). ethanol emulsion test for fats and oils
●​ Solution: Ethanol
●​ Positive: cloudy/milky
●​ Negative: no change
➢​ You add the test sample to a concentrated ethanol solution. You put the resulting mixture
into a test tube of distilled water, close it, and shake it around. If a cloudy emulsion
forms, fats are present; if not, there are no fats.
B5 - Enzymes
Enzymes: proteins that are involved in all metabolic reactions, where they function as biological catalysts
Activation energy: is the minimum amount of energy that particles (like enzyme and substrate
molecules) need to have when they collide in order for a reaction to happen.

-​ Investigate and describe the effect of changes in temperature and pH on enzyme activity
-​
-​ Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy,
shape and fit, frequency of effective collisions and denaturation
-​
➢​ The temperature an enzyme works best at is its ‘optimum temperature’.
➢​
●​ The lower the temperature (when lower than optimum temperature), the slower the enzyme
works

○​ The kinetic energy of enzyme and substrate molecules is reduced.​

○​ This means fewer collisions between enzymes and substrates.​

○​ Even when they do collide, they may not have enough energy to react.(energy must be
bigger than activation energy for reaction)​

○​ Result: Slower rate of reaction.

●​ the higher the temperature (when higher than optimum temperature), the less the enzyme
works.
○​ Enzymes begin to denature.​

○​ The bonds holding the enzyme’s 3D shape (especially hydrogen bonds) break.​

○​ The active site changes shape (no longer complementary to the substrate).​

○​ Result: The enzyme can no longer function — reaction rate drops.

 ○​
●​ At the Optimum Temperature:
○​ Enzyme and substrate molecules have maximum useful kinetic energy.​

○​ They move quickly and collide more frequently.​

○​ More collisions happen with enough energy to overcome the activation energy.
○​
○​ More collisions = higher probability of successful collisions
○​
○​ The active site of the enzyme is still in the correct shape (not denatured).​

○​ Result: Highest rate of successful enzyme-substrate collisions → fastest reaction rate.

-​ Explain the effect of changes in pH on enzyme activity in terms of shape and fit and
denaturation

➢​ The pH an enzyme works best at is its ‘optimum pH’.

The lower the pH (when lower than optimum), the less the enzyme functions; the higher the pH (when
higher than optimum), the less the enzyme works.

●​ Why does enzyme activity drop when pH is too low or too high?
○​ Enzymes have a specific active site that fits their substrate like a key in a lock.

○​ When the pH is lower or higher than the optimum, it changes the shape of the enzyme.

○​ This causes the active site to become altered, so the substrate no longer fits.

○​ If the change is too great, the enzyme becomes denatured — this means the shape change
is permanent, and the enzyme can no longer work.
Describe and explain enzyme action with reference to: the active site, enzyme–substrate complex,
substrate and product

1.​ Substrate – This is the specific molecule that the enzyme acts on.
2.​ The enzyme has a special region called the active site, which has a shape that is complementary
to the substrate — like a key fitting into a lock.
3.​ When the substrate binds to the active site, they form an enzyme–substrate complex.
●​ This is a temporary structure where the enzyme holds the substrate in place to help the
reaction occur.
4.​ The enzyme lowers the activation energy needed for a reaction, allowing the substrate to be
converted into product(s) more easily.
5.​ The product is then released from the enzyme, and the enzyme remains unchanged and can be
used again.
Describe and explain the specificity of enzymes in terms of the complementary shape and fit of the
active site with the substrate:

Enzymes are specific to one particular substrate because their active site has a shape that is
complementary to the shape of that substrate — like a key fitting into a lock.

Only the correct substrate can bind to the enzyme's active site to form an enzyme–substrate complex. If
the substrate doesn't match the shape of the active site, it cannot bind, and the enzyme cannot catalyse the
reaction.

This is known as enzyme specificity.

B6 - Plant nutrition
B6.1 Photosynthesis
Photosynthesis: the process by which plants synthesise carbohydrates from raw materials using energy
from light

Word equation for photosynthesis:

carbon dioxide + water → glucose + oxygen in the presence of light and chlorophyll
Chlorophyll: a green pigment that is found in chloroplasts

Balanced equation for photosynthesis

Investigate and understand the need for chlorophyll, light and carbon dioxide for photosynthesis

Chlorophyll:

●​ Take a potted plant with variegated leaves (leaves that have both green and white patches, like the
leaf on the left) and destarch the plant by keeping it in complete darkness for two days (about 48
hours).

●​ Place it in sunlight for a few days, so that it can form some new starch. Finally, perform the starch
test on one of the leaves (add a few drops of iodine to the leaf.)

●​ The green parts (i.e. the parts with chlorophyll) will turn blue-black, and the white parts will be
orange-brown. This shows that starch is only formed where chlorophyll is present. Hence,
photosynthesis can only occur in the presence of chlorophyll.

Light:

●​ Destarch a plant.
●​
●​ Cut out a strip of opaque black paper and clip it a section of one of the leaves, as shown.
●​
●​ Leave the plant in sunlight for a few days.
●​
●​ Perform the starch test and observe.
●​
●​ The areas that turn blue-black (and hence contain starch) are the areas exposed to sunlight, and
the orange-brown area was the section covered by paper. This shows that light is necessary for
photosynthesis.

Carbon dioxide:

●​ Destarch two potted plants.

●​
 ●​ Cover both plants in transparent plastic bags; place a petri dish of sodium hydrogencarbonate in
one, and a petri dish of soda lime in the other (as shown in the diagram). Sodium
hydrogencarbonate gives off carbon dioxide, and soda lime absorbs carbon dioxide from the air.
●​
●​ Leave these two plants in sunlight for a day (at least 6 hours). Perform the starch test on a leaf
from each plant.
●​
●​ You will find that the leaf from the plant with sodium hydrogencarbonate turns blue-black, and
the leaf from the plant with soda lime turns orange-brown. This shows that carbon dioxide is
necessary for photosynthesis.

The importance of chlorophyll:​

●​ Transfers energy from light into energy in chemicals, for the synthesis of carbohydrates

Outline the subsequent use and storage of the carbohydrates made in photosynthesis:

(a). starch as an energy store

(b). cellulose to build cell walls

(c). glucose used in respiration to provide energy

(d). sucrose for transport in the phloem

(e). nectar to attract insects for pollination

Explain the importance of:

●​ Nitrate ions for making amino acids
Proteins are made up of amino acids. Each amino acid has at least one amine group (-NH2), and plants get
the nitrogen for this amino acid synthesis from nitrate ions. Protein synthesis is vital for plants to stay
alive – proteins make up enzymes, hormones, are used for growth and repair, etc.

●​ Magnesium ions for making chlorophyll

Magnesium forms the central ion in a chlorophyll molecule. Chlorophyll is essential for photosynthesis.

Understand and describe the effects of varying light intensity, carbon dioxide concentration and
temperature on the rate of photosynthesis