GCSE Biology Paper One Summary

Cell Structure & Microscopy

All life consists of cells.

All living organisms are composed of cells, which can be broadly categorised into two types: eukaryotic and prokaryotic.

Eukaryotic Cells

are generally larger and more complex. They are characterised by the presence of a nucleus which houses their DNA.

Animal Cells

are examples of eukaryotic cells and contain several key organelles:

• Nucleus: Contains the cell's genetic material (DNA).

• Cytoplasm: A jelly-like substance where most chemical reactions occur.

• Cell Membrane: Controls the movement of substances into and out of the cell.

• Mitochondria: The site of aerobic respiration, where energy is released.

• Ribosomes: Responsible for protein synthesis.

Plant Cells 🪴

are also eukaryotic and include all the components of animal cells, plus three additional structures:

• Cell Wall: Made of cellulose, providing structural support and protection.

• Permanent Vacuole: A large central sac containing cell sap, involved in maintaining turgor pressure.

• Chloroplasts: Contain chlorophyll and are the primary sites of photosynthesis.

Prokaryotic Cells

are smaller and simpler than eukaryotic cells. 

They lack a true nucleus and other membrane-bound organelles such as mitochondria.

Bacterial Cells

are a prime example of prokaryotes:

• Cell Membrane: Regulates passage of substances.

• Cytoplasm: Site of metabolic reactions.

• Ribosomes: For protein synthesis.

• Cell Wall: Provides structural support (not made of cellulose but peptidoglycan)

• DNA: Unlike eukaryotic cells, their DNA is usually a circular strand floating freely in the cytoplasm or

 in small rings called plasmids, rather than being enclosed in a nucleus.

Microscopy

• Light Microscopes:

  • Uses light to magnify images up to a lower magnification (up to x2000)

  • Offers a Lower resolution compared to electron microscopes

  • Cheap/affordable

  • Easy sample prep

  • Portable

  • Specimens can be living or dead

• Electron Microscopes:

  • Uses electrons for higher magnification (up to x2,000,000)

  • Offers a higher resolution and resolving power than light microscopes

  • Expensive

  • Complex sample prep

  • Large and installation means it can’t be moved

  • Specimens must be dead

• Magnification Formula:  Actual size / Image size​

Cell Differentiation & Specialisation

is the process by which a non-specialised cell (a stem cell) develops into a specialised cell with a specific function.

Specialised Cells  

Here are six examples of specialised cells:

1. Sperm Cells:

   • Function: Deliver male DNA to female DNA for reproduction.

   • Adaptations:

     • Numerous mitochondria for energy to swim.

     • Streamlined head for efficient movement.

     • Long tail for mobility.

     • Enzymes in the acrosome to digest the egg cell membrane.

2. Nerve Cells (Neurones):

   • Function: Transmit electrical messages throughout the body.

   • Adaptations:

     • Long to cover large distances.

     • Branched connections (dendrites) to form extensive networks.

3. Muscle Cells:

   • Function: Specialised for contraction.

   • Adaptations:

     • Long to allow for significant shortening.

     • Many mitochondria to provide ample energy for contraction.

4. Root Hair Cells (Plants):

   • Function: Absorb water and mineral ions from the soil.

   • Adaptations:

     • Long, thin root hairs significantly increase their surface area for efficient absorption.

     • Many mitochondria to move mineral ions via active transport

5. Phloem Cells (Plants):

   • Function: Form phloem tubes to transport sugars and food substances up and down the plant.

   • Adaptations: Joined end-to-end; living cells.

6. Xylem Cells (Plants):

   • Function: Form xylem tubes to transport water and minerals upwards from the roots to the leaves.

   • Adaptations: Dead cells strengthened by lignin, forming hollow tubes.

Chromosomes

are structures found within the nucleus of cells, consisting of tightly coiled DNA.

• Human Body Cells: Contain 46 chromosomes, arranged in 23 pairs. One chromosome from each pair is inherited from each parent.

• Sex Cells (Gametes): Contain half the number of chromosomes, i.e., 23 unpaired chromosomes.

Cell Cycle & Mitosis 

The cell cycle is a series of events that cells undergo to divide and produce two genetically identical diploid daughter cells.

1. Growth and DNA Replication:

   • Cells increase the number of sub-cellular structures (e.g., mitochondria, ribosomes).

   • The cell's DNA is replicated (copied).

2. Mitosis:

   • The replicated chromosomes align at the centre of the cell.

   • They are then pulled apart to opposite ends of the cell.

3. Cell Division/Cytokinesis:

   • New membranes form around each set of chromosomes, creating two new nuclei.

   • The cytoplasm and cell membrane then divide, resulting in two genetically identical daughter cells.

Stem Cells & Their Uses

are undifferentiated cells that have not yet specialised and can develop into various cell types.

Human Stem Cells 

Humans have two main types of stem cells:

1. Embryonic Stem Cells:

   • Found in human embryos.

   • Totipotent/Pluripotent: Can differentiate into absolutely any type of body cell

2. Adult Stem Cells:

   • Found in certain tissues, such as bone marrow.

   • Multi-potent: Can only differentiate into a limited range of cell types (e.g., blood cells).

Medical Uses of Stem Cells

Stem cells offer potential treatments for various diseases:

• Embryonic Stem Cells: Show promise for treating conditions like diabetes and paralysis due to their ability to become any cell type.

• Adult Stem Cells: Can be used to replace faulty blood cells (e.g., in conditions like leukaemia).

Therapeutic Cloning

This technique involves creating an embryo with the same DNA as a patient. 

The stem cells from this embryo can then be used to treat diseases without the risk of immune rejection, 

as they are genetically identical to the patient.

1. Take a body cell from patient (has full DNA)

2. Take an egg cell from donor and remove nucleus

3. Insert patient’s nucleus (DNA) into empty egg

4. Egg is stimulated to divide → forms an early embryo (blastocyst)

5. Stem cells are taken and used to grow replacement tissues

👉 Result: cells match patient → no immune system rejection

Ethical Considerations

Stem cell research, particularly involving embryos, is controversial:

• Arguments Against: Some argue that using embryos for research destroys potential human lives.

• Arguments For: Others contend that the potential benefits for suffering patients outweigh the ethical concerns surrounding an embryo.

Meristem Cells

Plants also possess stem cells, located in meristem tissue at the tips of shoots and roots.

• Plant stem cells can differentiate into any type of plant cell.

• Uses: Can be used for cloning plants, which is beneficial for:

  • Preserving rare plant species.

  • Producing crops with desirable traits rapidly and in large quantities.

Transport in Cells

Diffusion

  is the net movement of particles from an area of high concentration to an area of low concentration down/along the concentration gradient.

• It is a passive process, meaning it does not require energy.

• Factors Increasing Rate of Diffusion:

  • Increased Temperature: Particles have more kinetic energy.

  • Increased Concentration Gradient: A larger difference in concentration between two areas leads to faster diffusion.

  • Increased Surface Area to Volume Ratio: More surface available relative to the volume for exchange.

Surface Area to Volume Ratio

• Smaller organisms typically have a larger surface area to volume ratio.

  • Example: A 1m cube has a ratio of 6:1, while a 2m cube has a smaller ratio of 3:1.

• This high ratio allows small organisms (e.g., bacteria) to exchange substances efficiently purely by diffusion.

• Larger organisms (animals, plants) have a small surface area to volume ratio, hence they require specialised exchange surfaces.

Exchange Surfaces

Four key exchange surfaces:

1. Alveoli (Lungs): For gas exchange in mammals.

2. Leaves (Plants): For gas exchange and photosynthesis.

3. Villi (Small Intestines): For nutrient absorption.

4. Gills (Fish): For gas exchange in aquatic environments.

These surfaces are adapted for efficiency by:

• Having thin membranes for a short diffusion pathway.

• Having a large surface area to maximise diffusion.

• Some are ventilated (e.g., lungs) to maintain a steep diffusion gradient.

Osmosis

is a special type of diffusion involving water. It is the net movement of water particles 

from an area of high water concentration to an area of low water concentration

 across a partially permeable membrane.

• A partially permeable membrane only allows small particles like water to pass through.

• Example: Root hair cells absorb water from the soil by osmosis, as water moves from a high concentration in the soil to a lower concentration inside the root hair cell.

Active Transport

   is the movement of particles from an area of low concentration to an area of high concentration, against the concentration gradient.

• This process requires energy, typically derived from respiration.

• Example 1: Root hair cells absorb mineral ions from the soil via active transport because the concentration of mineral ions in the soil is often lower than inside the cell.

• Example 2: Humans absorb glucose from the gut into the bloodstream using active transport when the glucose concentration in the gut is lower than in the blood.

Organisation of Life

Living organisms are organised in a hierarchical manner:

1. Cells: The basic building blocks of all living things.

2. Tissues: Groups of similar cells that work together to perform a specific function (e.g., muscle tissue, epidermal tissue).

3. Organs: Complex structures composed of different tissues working together to carry out specific tasks (e.g., heart, stomach, leaf).

4. Organ Systems: Groups of organs that work together to perform major functions (e.g., digestive system, circulatory system).

5. Organism: A complete living being formed by multiple organ systems working in coordination.

Enzymes

Enzymes are biological catalysts – large proteins that speed up specific biochemical reactions without being used up or altered in the process.

• Structure: Enzymes are folded into unique 3D shapes, featuring an indentation called an active site.

• Function:

  • A specific molecule, called the substrate, fits precisely into the active site.

  • The enzyme then facilitates the breakdown of the substrate into products.

  • Once products are released, the active site is ready for new substrates (Lock and Key Model).

• Specificity: Each enzyme typically acts on only one specific type of substrate.

Factors Affecting Enzyme Activity

1. Temperature:

   • As temperature increases, enzyme activity generally increases due to more frequent collisions between enzyme and substrate.

   • There is an optimum temperature at which the enzyme works most efficiently.

   • Beyond the optimum, high temperatures cause the enzyme to denature (its active site changes shape), meaning the substrate can no longer bind, and activity decreases rapidly.

2. pH:

   • Enzymes have an optimum pH range where they function best.

   • If the pH becomes too acidic or too alkaline (too high or too low), the enzyme will denature, altering the active site and reducing its efficiency.

Digestive Enzymes

• are biological catalysts which break down food into small soluble molecules without being consumed/used up or altered in the process

      - Three main types of digestive enzymes :

• Amylase breaks down Starch → Glucose (found in salivary glands, pancreas, small intestine)

• Protease breaks down Proteins → amino acids (found in stomach, pancreas, small intestine)

• Lipase breaks down Lipids → fatty acids + glycerol (found in pancreas, small intestine)

• Bile from the liver, neutralises hydrochloric acid + emulsifies fats to increase the surface area for the lipase enzyme to act on it.

The Digestive System

The human digestive system is a complex organ system responsible for breaking down food and absorbing nutrients.

1. Mouth:

   • Mechanical digestion: Teeth chew food.

   • Chemical digestion: Saliva contains amylase, beginning the breakdown of carbohydrates into simple sugars.

2. Oesophagus: Food travels down to the stomach.

3. Stomach:

   • Produces protease enzymes to break down proteins into amino acids.

   • Produces hydrochloric acid:

     • Provides the optimum pH for protease enzymes.

     • Kills most bacteria ingested with food.

4. Liver: Produces bile:

   • Neutralises stomach acid, creating an alkaline environment for enzymes in the small intestine.

   • Emulsifies fats: Breaks large fat globules into smaller droplets, increasing surface area for lipase action.

5. Gallbladder:

   • Stores bile produced by the liver.

   • Releases bile into the small intestine when fatty food arrives.

6. Pancreas: Produces all three types of digestive enzymes (amylase, protease, lipase) and releases them into the small intestine.

7. Small Intestine:

   • Further breakdown of food by enzymes from the pancreas and intestinal walls.

   • The primary site where broken-down food particles (nutrients) are absorbed into the blood through structures called villi.

8. Large Intestine:

   • Excess water is absorbed from the remaining undigested material.

9. Rectum: Stores leftover undigested material (faeces) before elimination.

10. Anus: Excretes faeces and controls bowel movements

Food Tests

• Starch (Iodine test): orange-brown → blue-black

• Reducing sugars (Benedict’s test): blue → green/yellow/orange/brick-red

• Protein (Biuret test): blue → lilac/purple

• Lipids (Ethanol emulsion test): colourless → white/cloudy (milky) emulsion

The Circulatory System

The circulatory system distributes substances throughout the body and is primarily composed of the blood, blood vessels, and the heart.

Blood Components

Blood is made of four main components:

1. Red Blood Cells:

   • Function: Carry oxygen.

   • Adaptations:

     • Contains haemoglobin, which binds to oxygen.

     • No nucleus, allowing more space for haemoglobin.

     • Biconcave shape and high surface area-to-volume ratio to maximise oxygen transport.

2. White Blood Cells:

   • Function: Fight infection as part of the immune system.

3. Platelets:

   • Function: Cell fragments involved in blood clotting to prevent excessive bleeding and infection.

4. Plasma:

   • The liquid component of blood.

   • Carries all other blood components, digested food, waste products, and hormones around the body.

The Heart

The heart is a muscular organ that pumps blood throughout the circulatory system.

Heart Structure and Blood Flow

• The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle.

• Blood flow is unidirectional, controlled by valves.

• The right side pumps deoxygenated blood to the lungs.

• The left side pumps oxygenated blood to the rest of the body.

  • The muscle wall of the left side is thicker and more muscular than the right, as it needs to pump blood at a much higher pressure over longer distances.

• Direction of blood flow through the circulatory system :

Vena Cava
↓
Right Atrium
↓
Right Ventricle
↓
Pulmonary Artery
↓
Lungs
↓
Pulmonary Vein
↓
Left Atrium
↓
Left Ventricle
↓
Aorta
↓
Body (organs/tissues)
↓
Vena Cava

Pacemaker

• Specialised cells in the right atrium act as the natural pacemaker, generating electrical impulses that regulate the heartbeat.

• If the natural pacemaker malfunctions, an artificial pacemaker can be implanted to take over this function.

Double Circulatory System

Humans have a double circulatory system:

1. Pulmonary Circuit: Carries deoxygenated blood from the heart to the lungs (for oxygenation) and then back to the heart.

2. Systemic Circuit: Carries oxygenated blood from the heart to all cells in the body and returns deoxygenated blood to the heart.

Blood Vessels

Three types of blood vessels:

1. Arteries:

   • Function: Carry blood away from the heart.

   • Characteristics:

     • Experience high pressure.

     • Thick, muscular walls to withstand pressure.

     • Narrow lumen (internal channel).

2. Veins:

   • Function: Carry blood towards the heart.

   • Characteristics:

     • Experience much lower pressure.

     • Thinner walls and a larger lumen.

     • Contain valves to prevent the back-flow of blood, especially against gravity.

3. Capillaries:

   • Function: Tiny blood vessels that facilitate the exchange of gases, nutrients, and waste products between blood and body cells.

   • Characteristics:

     • Only one cell thick walls to ensure a very short diffusion pathway for efficient exchange.

The Lungs & Gas Exchange

The lungs, located in the thorax, are responsible for gas exchange.

• Air enters through the trachea.

• The trachea divides into two bronchi.

• Bronchi further divide into smaller bronchioles.

• At the end of the bronchioles are tiny air sacs called alveoli, where gas exchange occurs efficiently due to their large surface area, thin walls, and rich blood supply.

Health & Disease

Cardiovascular Diseases (CVDs)

CVDs are diseases related to the circulatory system.

Coronary Heart Disease (CHD)

• Description: A disease affecting the coronary arteries, which supply blood and oxygen to the heart muscle.

• Cause: Blockage of coronary arteries due to a buildup of fatty material (atherosclerosis).

• Consequences: Can lead to chest pain (angina) and heart attacks.

Treatments for CHD

1. Stents:

   • Description: Small, expandable metal mesh tubes inserted into blocked arteries to hold them open.

   • Benefit: Keeps arteries open, improving blood flow.

2. Statins:

   • Description: A class of drugs that lower cholesterol levels in the blood.

   • Benefit: Reduces the buildup of fatty material in arteries.

   • Disadvantages: Must be taken regularly; can have side effects.

3. Artificial Hearts:

   • Description: Mechanical pumps used to temporarily support heart function when a patient's heart fails and a transplant is not immediately available.

   • Risk: Reduced risk of infection (due to man-made materials) but carries general surgical risks and risk of blood clots.

4. Faulty Heart Valves:

   • Treatment: Can be replaced with mechanical valves (man-made) or biological valves (from other mammals, like pigs).

Non-Communicable Diseases

• Diseases that cannot spread between organisms.

• Examples: Coronary Heart Disease, cancer, diabetes.

Risk Factors

Factors that increase the likelihood of developing a disease:

• Lifestyle:

  • Lack of exercise → CVD.

  • Obesity → Type 2 diabetes.

• Substances taken into the body:

  • Alcohol → Liver cancer, heart disease.

  • Smoking → Lung cancer, mouth cancer, heart disease.

• Genetic factors.

Cancer

• Description: Characterised by uncontrolled cell growth and division, leading to the formation of tumours.

Types of Tumours

1. Benign Tumours:

   • Non-cancerous.

   • Abnormal cells remain contained within one area (often within a membrane) and do not invade other parts of the body.

2. Malignant Tumours:

   • Cancerous.

   • Cells can spread to other parts of the body via the bloodstream or lymphatic system, forming secondary tumours.

Risk Factors for Cancer

• Smoking

• Obesity

• UV exposure

• Some viral infections (e.g., HPV)

Plant Tissues & Organs

Plants have various specialised tissues:

1. Waxy Cuticle

• Function: Creates a waterproof barrier over the surface of the leaf, reducing water loss by evaporation.

• Structure: A thin, waxy, transparent layer covering the epidermis of the leaf.

2. Upper Epidermis

• Function: Forms a protective outer layer and allows light to pass through to the palisade mesophyll for photosynthesis.

• Structure: A thin layer of tightly packed transparent cells located beneath the waxy cuticle.

• 3. Palisade Mesophyll Tissue

• Function: Main site of photosynthesis.

• Structure: Made of tightly packed elongated cells containing numerous chloroplasts to absorb large amounts of light.

4. Spongy Mesophyll Tissue

• Function: Facilitates gas exchange within the leaf.

• Structure: Made of loosely packed cells with large air spaces between them to allow diffusion of gases such as carbon dioxide and oxygen.

5. Xylem Tissue

• Function: Transports water and mineral ions from the roots to the leaves.

• Structure: Made of dead hollow cells strengthened with lignin, forming continuous tubes.

6. Phloem Tissue

• Function: Transports dissolved sugars and other food substances around the plant in both directions.

• Structure: Made of living cells joined end to end with perforated end walls called sieve plates.

7. Lower Epidermis

• Function: Forms a protective outer layer and contains stomata for gas exchange.

• Structure: A thin layer of cells on the lower surface of the leaf containing stomata and guard cells.

8. Meristem Tissue

• Function: Produces new cells for plant growth by mitosis.

• Structure: Made of unspecialised stem cells that can divide and differentiate into specialised plant cells.

Stomata and Guard Cells

• The lower epidermis of leaves contains many small pores called stomata.

• Each stoma is flanked by two guard cells, which regulate its opening and closing.

  • Daytime (high light intensity): Guard cells absorb water, become turgid, and pull apart to open the stomata, allowing gas exchange.

  • Nighttime (low light intensity): Guard cells lose water, become flaccid, and close the stomata, reducing gas exchange and water loss.

💧 Transpiration in Plants

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, primarily leaves, stems and flowers. This process is mainly driven by evaporation and diffusion of water from the plant surface, mostly through the stomata.

Factors Affecting Transpiration Rate

The rate of transpiration can increase due to:

• Increased Light Intensity: Stomata open wider in more light to allow for gas exchange, increasing water vapour release.

• Higher Temperature: Water molecules gain more kinetic energy, increasing the rate of evaporation and diffusion.

• Increased Air Flow Rate (Wind): Moving air blows away water vapour outside the leaf, maintaining a steep concentration gradient and increasing diffusion.

• Decreased Humidity: A lower concentration of water vapour in the surrounding air increases the concentration gradient between the leaf and the air, speeding up diffusion.

Measuring Transpiration

A potometer can be used to measure the rate of water uptake by a plant, which is an indirect measure of transpiration. This involves timing how long it takes for an air bubble to move a certain distance in a capillary tube.

Communicable Diseases

are infectious diseases that can spread between organisms,

caused by pathogens (pathogens are harmful microorganisms that can cause disease)

Types of Pathogens

1. Bacteria: Single-celled living organisms that can produce toxins, causing illness.

2. Viruses: Non-living entities that reproduce inside body cells, causing them to burst and spread.

3. Protists: Single-celled eukaryotes that can be spread by vectors (e.g., mosquitoes spreading malaria).

4. Fungi: Can be single-celled or multicellular, often causing infections.

Preventing Disease Spread

• Good Hygiene: Hand washing, proper sanitation.

• Destroying Vectors: Using insecticides to kill mosquitoes that carry diseases.

• Isolating Infected Individuals: To limit contact and transmission.

• Vaccination: To build immunity within populations.

Human Defences Against Pathogens : S.N.A.S.I

1. Skin: Acts as a physical barrier and produces antimicrobial substances.

2. Nose: Hairs and mucus trap pathogens.

3. Air Passages (Trachea, Bronchi): Lined with mucus and cilia (hair-like structures) that sweep mucus and pathogens up to the throat, where they are swallowed.

4. Stomach: Produces hydrochloric acid to kill most ingested pathogens.

5. Immune System

If pathogens enter the blood, the immune system responds:

• Phagocytes (White Blood Cells): Carry out phagocytosis, engulfing and digesting pathogens.

• Lymphocytes (White Blood Cells):

  • Produce antibodies that bind to pathogens, marking them for destruction.

  • Produce antitoxins that neutralise toxins produced by bacteria.

  • After an infection, some lymphocytes remain as memory cells. If the same pathogen re-enters the body, memory cells rapidly produce antibodies, preventing symptoms (immunity).

Vaccinations

Vaccinations involve injecting a dead or inactive form of a pathogen into the body.

• This triggers the lymphocytes to produce antibodies and memory cells.

• The body becomes immune to the disease without actually experiencing the full illness.

• If the real pathogen enters later, the memory cells rapidly produce a large quantity of antibodies, preventing the disease.

• Example: MMR vaccine (Measles, Mumps, Rubella).

Advantages of Vaccines

• Prevent widespread disease.

• Can lead to herd immunity.

Disadvantages of Vaccines

• Potential side effects.

• Not 100% effective.

Medical Treatments

Painkillers

• Examples: Paracetamol, aspirin.

• Function: Manage the symptoms of a disease (e.g., pain, fever) but do not kill the pathogen causing the disease.

Antibiotics

• Function: Kill bacteria (or inhibit their growth).

• Ineffective against viruses because viruses reproduce inside host cells, making them difficult to target without harming the host.

• Antibiotic Resistance:

  • Overuse of antibiotics leads to bacteria evolving resistance.

  • Resistant bacteria survive and reproduce, making antibiotics ineffective.

  • To combat this: Doctors are advised to prescribe antibiotics only when necessary and patients must complete the full course to reduce the chance of resistance developing.

Origin of Drugs

Many modern drugs are derived from natural sources:

• Aspirin: From willow bark.

• Penicillin: From mould.

• Digitalis (for heart conditions): From foxgloves.

Drug Development Stages : C.A.V.I.P

Drugs undergo rigorous testing before public use:

1. Pre-clinical Trials:

   • Initial tests: On human cells and tissues in the laboratory.

   • Animal tests: To assess efficacy, toxicity, and dosage.

     • Efficacy: How well the drug works.

     • Toxicity: How harmful the drug is.

     • Dosage: How much and how often the drug should be taken.

2. Clinical Trials (on humans):

   • Phase 1: Low doses given to healthy volunteers to check for side effects and determine safe dosage range. Dose is gradually increased to find the optimum.

   • Phase 2/3: Drug given to patients.

     • Patients are split into two groups: one receives the new drug, the other receives a placebo (an inactive substance that looks like the drug).

     • Blind trials: Patient doesn't know if they're receiving the real drug or placebo (prevents psychological bias).

     • Double-blind trials: Neither the patient nor the doctor knows who received what (further reduces bias).

3. Peer Review:

   • After successful clinical trials, other scientists review the methods, results, and conclusions to ensure the validity and reliability of the trial.

Photosynthesis (Opposite of Respiration)

Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen, using light energy from the sun.

• It is an endothermic process (absorbs energy).

• Location: Primarily occurs in chloroplasts within plant cells, which contain chlorophyll to absorb sunlight.

• Equation: Carbon dioxide + water → glucose + oxygen

  • 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂ 

Uses of Glucose from Photosynthesis : S.C.A.R.F

The glucose produced by plants can be used for:

• Starch: Stored as an insoluble carbohydrate for energy storage.

• Cellulose: Synthesised for cell walls.

• Amino Acids: Combined with nitrate ions to make amino acids, which are then used to build proteins.

• Respiration: To release energy for metabolic processes.

• Fats/Lipids: Stored in seeds as an energy reserve.

Factors Affecting Photosynthesis Rate

Photosynthesis is affected by limiting factors:

1. Light Intensity:

   • As light intensity increases, the rate of photosynthesis increases up to a point.

   • Eventually, it plateaus because another factor (CO2 concentration or temperature) becomes limiting.

2. Carbon Dioxide Concentration:

   • As CO2 concentration increases, the rate of photosynthesis increases up to a point.

   • It then plateaus because another factor (light intensity or temperature) becomes limiting.

3. Temperature:

   • Rate increases with temperature up to an optimum temperature.

   • Above the optimum, the enzymes involved in photosynthesis (like all enzymes) begin to denature, and the rate decreases rapidly.

Respiration (Opposite of Photosynthesis)

is a chemical process that transfers energy by breaking down glucose. It is an exothermic process (releases energy).

• Energy released is used for:

  • Maintaining body temperature (keeping warm).

  • Muscle contraction for movement.

  • Building larger molecules from smaller ones.

Aerobic Respiration

• Definition: Respiration that occurs with oxygen.

• Location: Mainly in the mitochondria.

• Equation: Glucose + Oxygen → Carbon Dioxide + Water+ Energy

  • C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O 

• Releases a large amount of energy.

Anaerobic Respiration

• Definition: Respiration that occurs without oxygen.

• Releases significantly less energy than aerobic respiration.

• In Human Muscle Cells:

  • Glucose → Lactic Acid + Energy

• In Plants and Yeast Cells (Fermentation):

  • Glucose → Ethanol + Carbon Dioxide + Energy

  • Used in bread-making (CO2 causes bread to rise) and alcoholic drinks (ethanol makes them alcoholic).

Respiration During Exercise

• During exercise, muscles contract more, requiring more energy.

• Increased breathing rate, breath volume, and heart rate deliver more oxygen for aerobic respiration.

• Vigorous exercise (e.g., sprinting): Oxygen supply may be insufficient for aerobic respiration, so anaerobic respiration occurs.

  • Leads to lactic acid buildup in muscles, causing pain and muscle fatigue (reduced efficiency of contraction).

• Oxygen Debt: After exercise, the body has an oxygen debt that needs to be repaid to clear the accumulated lactic acid.

  • Breathing and heart rate remain high.

  • Lactic acid is transported to the liver, where it is converted back into glucose or oxidised.

Metabolism   

is the sum of all chemical reactions occurring in an organism, regulated by enzymes. Key metabolic reactions include:

• Joining glucose molecules to make starch (plants), cellulose (plants), or glycogen (animals).

• Forming lipids from one glycerol and three fatty acids.

• Forming amino acids from glucose and nitrate ions.

• Breaking down excess proteins into urea.

• Breaking down glucose in respiration to transfer energy.