Final biology test

Macromolecules

Macromolecules are large carbon-based molecules found in all living things.
They are made up of smaller building blocks called monomers, which link together to form polymers.

4 Types of Organic Macromolecules

1. Carbohydrates

   • Monomer: Monosaccharide (e.g., glucose)

   • Polymer: Polysaccharide (e.g., starch, cellulose, glycogen)

   • Elements: Carbon (C), Hydrogen (H), Oxygen (O)

   • Function: Main source of energy; structural component in plant cell walls (cellulose)

   • Examples:

     • Monosaccharide: Glucose

     • Disaccharide: Sucrose, Maltose

     • Polysaccharide: Cellulose (plants), Glycogen (animals)

   • Food examples: Bread, pasta, pizza

2. Proteins

   • Monomer: Amino acid

   • Polymer: Polypeptide (protein)

   • Elements: C, H, O, Nitrogen (N)

   • Functions:

     • Build body structures

     • Enzymes (speed up chemical reactions)

     • Immune defense (antibodies)

   • Examples: Enzymes, Collagen, Hemoglobin, Antibodies

   • Bond type: Peptide bonds

   • Food examples: Eggs, meat, fish, chicken

3. Lipids

   • Not true polymers (but made of glycerol + 3 fatty acids)

   • Elements: C, H, O

   • Properties: Non-polar (don’t mix with water)

   • Functions:

     • Store energy

     • Insulation

     • Make up cell membranes

   • Types:

     • Fats (saturated) – all single bonds (C–C–C–C)

     • Oils (unsaturated) – have double bonds (C=C–C)

     • Waxes, Hormones

   • Food examples: Butter, oil, avocado, cheese

4. Nucleic Acids

   • Monomer: Nucleotide

   • Polymer: DNA or RNA

   • Elements: C, H, O, N, Phosphorus (P)

   • Function:

     • Store genetic information

     • Direct protein synthesis

Other Key Points

• Carbon Atom Properties:

  • Has 4 valence electrons → can form 4 bonds

  • Can form:

    • Straight chains (C–C–C)

    • Branched chains

    • Rings

• Bond Type:

  • Monomers connect to form polymers through chemical bonds (not hydrogen bonds for all – mostly covalent and peptide bonds, depending on the macromolecule).

• Common Elements in Living Things (about 95% of body weight):

  • Carbon (C)

  • Hydrogen (H)

  • Oxygen (O)

  • Nitrogen (N)

  • Phosphorus (P)

  • Sulfur (S)

Enzymes

What Are Enzymes?

• Enzymes are proteins that act as biological catalysts.

• They speed up chemical reactions in the body without being used up or changed.

• Found in all living organisms.

Function of Enzymes

• Involved in almost every chemical reaction in cells.

• They work by lowering the activation energy, which makes reactions happen faster.

• They turn substrates (reactants) into products.

Types of Enzyme Reactions

1. Degradation Reactions:

   • Break down large molecules into smaller ones.

   • Example: Protein → amino acids

2. Synthesis Reactions:

   • Build larger molecules from smaller ones.

   • Example: Amino acids → protein

Enzyme Structure and Composition

• Made mostly of 100–1000 amino acids.

• Enzymes have a specific 3D shape that is crucial for their function.

• The shape allows them to interact with specific substrates.

Specificity of Enzymes

• Enzymes have an active site, where the substrate binds.

• The active site fits only certain substrates – like a lock and key.

• Only the correct substrate will fit into the enzyme’s active site.

Factors That Affect Enzyme Activity

1. Temperature

   • Enzymes work best between 30–40°C.

   • High temperatures can cause denaturation (enzyme loses shape and stops working).

2. pH Level

   • Each enzyme works best at a specific pH.

   • Extreme pH levels can also cause denaturation.

3. Substrate Concentration

   • More substrate increases the rate of reaction, up to a point.

   • After all active sites are used (saturation), the rate no longer increases.

Summary of Enzyme Properties

• Made of proteins.

• Speed up reactions without being used up.

• Highly specific (each enzyme only works on one type of substrate).

• Work best at optimal temperature and pH.

• Can become denatured if conditions are not right.

Digestive System

What is Digestion?

Digestion is the process of breaking down large, insoluble food molecules into small, soluble molecules so they can be absorbed into the blood.

Examples:

• Carbohydrates → Simple sugars (e.g., glucose)

• Proteins → Amino acids

• Lipids (fats) → Fatty acids and glycerol

• Nucleic acids → Nucleotides

Two Types of Digestion

1. Mechanical Digestion

   • Physical breakdown of food

   • Examples: chewing, grinding, crushing

2. Chemical Digestion

   • Breaking food into molecules using enzymes and acids

   • Helps nutrients be absorbed into the bloodstream

   • Affected by temperature and ph

Organs of the Digestive System

Main Organs (food passes through):

• Mouth

• Oesophagus

• Stomach

• Small intestine

• Large intestine

Accessory Organs (help digestion but food doesn't pass through them):

• Salivary glands

• Liver

• Gallbladder

• Pancreas

Mouth

• Both mechanical and chemical digestion happens here

• pH: 6.5–7

• Saliva + food = bolus (soft, wet food ball)

• Enzyme produced:

  • Amylase → breaks down starch into sugar

Oesophagus

• A muscular tube that moves food from the mouth to the stomach

• Contains the epiglottis, a flap that prevents food from entering the windpipe

Stomach

• Breaks down proteins into amino acids

• Uses gastric juice, which contains:

  • Hydrochloric acid (HCl) → kills bacteria

  • Pepsin → breaks down proteins

• Food becomes chyme (partially digested mixture)

• pH: 1.5–3.5

Small Intestine

• Around 7 meters long

• Main site for digestion and absorption of nutrients

• Villi and microvilli (tiny projections) increase surface area to absorb more nutrients

• Nutrients are absorbed into blood capillaries, then sent to the liver

Large Intestine

• Absorbs water from leftover food

• Turns waste into solid feces

• Contains helpful bacteria like E. coli

Accessory Organs and Their Functions

• Salivary glands → produce saliva (with enzymes like amylase)

• Liver → makes bile to break down fats

• Gallbladder → stores bile

• Pancreas → produces:

  • Insulin (controls blood sugar)

  • Digestive enzymes (see below)

Digestive Enzymes and Their Functions

More Enzymes in the Digestive System

Mouth:

• Salivary amylase → starch to sugar

• Lingual lipase → starts fat digestion

• Lysozyme → breaks bacterial cell walls (kills bacteria)

Stomach:

• Gastric juice = HCl + pepsin

• Pepsin breaks protein into amino acids

Pancreas:

• Amylase → starch to monosaccharides

• Lipase → lipids to fatty acids and glycerol

• Trypsin → proteins to amino acids

• Nuclease → nucleic acids to nucleotides

Respiratory System

1. Breathing vs. Respiration

• Breathing: The physical movement of air in and out of the lungs.

• Respiration: A chemical reaction that happens in cells to release energy from glucose.

  • Aerobic respiration: Uses oxygen; produces more energy.

  • Anaerobic respiration: Does not use oxygen; produces less energy.

2. Functions of the Respiratory System

• Takes in oxygen for respiration.

• Removes carbon dioxide from the body.

• Filters, moistens, and warms incoming air.

• Regulates air temperature and moisture.

• Helps produce sound (voice).

• Allows the sense of smell.

• Enables gas exchange between the lungs and the bloodstream.

3. Main Organs of the Respiratory System

1. Nose/Nasal Cavity: Warms, moistens, and filters air.

2. Pharynx: Connects the nose and mouth to the larynx; passageway for air and food.

3. Larynx (Voice Box): Contains vocal cords; prevents food from entering the trachea.

4. Trachea (Windpipe): Carries air to and from the lungs; has rings of cartilage to keep it open.

5. Bronchi: Two tubes that branch off the trachea and carry air into each lung.

6. Bronchioles: Smaller branches of the bronchi that lead to the alveoli.

7. Alveoli: Tiny air sacs where gas exchange occurs (oxygen in, carbon dioxide out).

8. Diaphragm: Dome-shaped muscle that helps with breathing by moving up and down.

9. Intercostal Muscles: Between the ribs; help expand and contract the chest during breathing.

10. Lungs: Main organs where gas exchange happens.

4. How Breathing Works

Inhalation (Breathing In):

• Diaphragm contracts and moves down.

• Intercostal muscles contract and expand the chest.

• Chest volume increases, air pressure drops.

• Air rushes into the lungs.

Exhalation (Breathing Out):

• Diaphragm relaxes and moves up.

• Intercostal muscles relax, chest gets smaller.

• Chest volume decreases, air pressure rises.

• Air is pushed out of the lungs.

5. Adaptations of the Alveoli (for Gas Exchange)

• Large surface area: More space for gases to exchange.

• Thin walls: Only one cell thick, so gases can diffuse quickly.

• Moist lining: Helps gases dissolve and pass through.

• Surrounded by capillaries: Gases move easily between alveoli and blood.

• Elastic walls: Expand and contract with each breath.

• Rich blood supply: Maintains strong concentration gradients for gas exchange.

Nervous System

What is the Nervous System?

The nervous system is the body’s communication network. It allows the brain to send and receive messages from the rest of the body so you can move, feel, think, and react.

Two Main Parts of the Nervous System

1. Central Nervous System (CNS)

   • Made up of the brain and spinal cord.

   • Acts as the control center of the body.

2. Peripheral Nervous System (PNS)

   • Includes all the nerves outside the brain and spinal cord.

   • Sends messages between the CNS and the rest of the body.

Functions of the Nervous System

• Sends messages (e.g., “move your hand”).

• Receives information (e.g., when you feel cold or pain).

• Controls automatic actions (e.g., heartbeat, blinking, breathing).

Example: If you step on a sharp object:

• Your foot sends a message to the brain saying “Pain!”

• The brain responds with “Move your foot!”

• This happens almost instantly.

Three Main Functions

1. Sensory Input

   • Gathers information from senses (eyes, ears, skin, etc.).

   • Example: You see a ball coming toward you.

2. Integration

   • The brain processes the information and decides what to do.

   • Example: Your brain decides to catch the ball.

3. Motor Output

   • Sends signals to muscles or glands to react.

   • Example: Your hand reaches out to catch the ball.

Summary: Sense → Think → Act

How the Nervous System Works (Step-by-Step)

1. Stimulus – A change in the environment (e.g., touching a hot stove).

2. Receptor – Special cells detect the stimulus (e.g., skin detects heat).

3. Sensory Neuron – Carries the message to the brain or spinal cord.

4. Coordinator (CNS) – Brain or spinal cord processes the information.

5. Motor Neuron – Sends response message to muscles or glands.

6. Effector – Muscle or gland that carries out the response.

7. Response – The action (e.g., pulling your hand away).

Flow Chart:
Stimulus → Receptor → Sensory Neuron → CNS → Motor Neuron → Effector → Response

What is a Neuron?

A neuron is a special cell that carries messages in the nervous system. It acts like a messenger.

Parts of a Neuron

• Dendrites: Receive messages from other neurons.

• Cell Body: Processes the message.

• Nucleus: Controls the cell and contains genetic material.

• Axon: Sends the message along the neuron.

• Myelin Sheath / Schwann Cells: Cover the axon and help messages travel faster.

• Axon Terminals: Pass the message to the next cell.

• Synapse: A tiny gap between neurons where chemical messengers (neurotransmitters) carry the signal across.

How a Neuron Sends a Message

1. A signal is received by the dendrites.

2. The cell body processes it.

3. If strong enough, it moves down the axon.

4. It crosses the synapse using neurotransmitters to reach the next neuron or muscle.

Types of Neurons

1. Sensory Neurons (Afferent)

   • Carry messages from receptors to the brain/spinal cord.

   • Example: Sends message when you touch something hot.

2. Interneurons (Relay Neurons)

   • Found in the brain/spinal cord.

   • Connect sensory neurons to motor neurons.

   • Example: Brain processes the message and decides what to do.

3. Motor Neurons (Efferent)

   • Carry instructions from the brain/spinal cord to muscles or glands.

   • Example: Tell your hand to move away from the hot object.

Flow:
Sensory Neuron → Interneuron → Motor Neuron
Or simply: Sense → Decide → React

Photosynthesis

1. Definition

Photosynthesis is a chemical reaction that occurs in green plant cells. It uses light energy to convert carbon dioxide (from the air) and water (from the soil) into glucose (a type of sugar) and oxygen.

• The term “photosynthesis” means “putting together with light” (from Greek: photo = light, synthesis = putting together).

2. Word and Chemical Equation

Word Equation:

Carbon dioxide + Water → Glucose + Oxygen
(in the presence of light energy and chlorophyll)

Chemical Equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

3. Requirements for Photosynthesis

• Carbon dioxide (CO₂) – enters the leaf through stomata

• Water (H₂O) – absorbed from the soil by roots

• Sunlight – provides energy for the reaction

• Chlorophyll – green pigment in chloroplasts that captures light energy

4. Where It Happens

• Photosynthesis takes place in chloroplasts in the cells of green plants.

• Chlorophyll, found in chloroplasts, absorbs sunlight to start the reaction.

5. Products of Photosynthesis

• Glucose (C₆H₁₂O₆): Used as energy, stored as starch, or converted into other substances.

• Oxygen (O₂): Released as a waste product into the air.

6. Structure of a Leaf and Adaptations for Photosynthesis

• Wide and flat: Increases surface area to absorb more light.

• Thin: Allows gases to reach cells quickly.

• Stomata: Tiny pores for gas exchange.

• Veins: Transport water to the leaf and glucose away

• Chlorophyll: Absorbs sunlight efficiently.

7. Factors Affecting the Rate of Photosynthesis

• Light intensity: More light increases the rate until it levels off or causes damage.

• Carbon dioxide concentration: Higher levels increase the rate up to a certain point.

• Temperature: Moderate warmth increases the rate, but too much heat destroys enzymes and stops the reaction.

8. Uses of Glucose in Plants

• Energy: Broken down in respiration.

• Stored as starch: Starch is insoluble and less reactive, ideal for storage.

• Making other substances:

  • Proteins (needs nitrogen from soil)

  • Fats and oils

  • Sucrose: For transport

  • Cellulose: For cell walls

  • Chlorophyll

9. Testing for Starch (to prove photosynthesis happened)

• Step 1: Boil the leaf in water to break cell membranes (2 minutes) .

• Step 2: Remove chlorophyll using alcohol (2 minutes).

• Step 3: Add iodine solution:

  • Blue-black = starch present (positive test)

  • Orange-brown = no starch (negative test)

Ecology

Key Definitions

• Species: A group of organisms that can reproduce with each other and have fertile offspring.

• Population: A group of the same species living in the same place at the same time.

• Community: Different populations living and interacting in one area.

• Habitat: The natural place where an organism lives.

• Ecosystem: A community of living things and the non-living things in their environment (such as air, water, and soil).

• Ecology: The study of how living things interact with each other and with their environment.

Relationships Between Species and Environments

• A population is made of individuals of one species.

• A community is made of many populations living together.

• An ecosystem includes both the community and the non-living parts of the environment.

• A change in one population often shows a change in the ecosystem.

Feeding Types

• Producers: Make their own food using sunlight (plants, some bacteria).

• Consumers: Eat other organisms because they cannot make their own food.

  • Herbivores: Eat only plants.

  • Carnivores: Eat only animals.

  • Omnivores: Eat both plants and animals.

Feeding Types (with Examples)

• Producers: Make their own food using sunlight (photosynthesis) or chemicals.
  Examples: Grass, seaweed, algae, oak trees, cyanobacteria.

• Consumers: Cannot make their own food. They must eat other organisms.

  • Herbivores: Eat only producers (plants).
    Examples: Cow, deer, rabbit, caterpillar.

  • Carnivores: Eat only other consumers (animals).
    Examples: Lion, fox, hawk, spider.

  • Omnivores: Eat both producers and consumers (plants and animals).
    Examples: Humans, bears, raccoons, chickens.

Food Chains

• A food chain shows how energy moves from one organism to another.

• It always starts with a producer.

• Example: Leaf → Caterpillar → Bird → Fox

• Each arrow means "is eaten by".

Consumer Levels in a Food Chain

• Producer: Makes its own food.

• Primary consumer: Eats the producer (usually a herbivore).

• Secondary consumer: Eats the primary consumer (usually a carnivore).

• Tertiary consumer: Eats the secondary consumer.

Food Webs

• A food web shows how multiple food chains are connected.

• Most animals are part of many food chains.

• Having more than one food source makes animals more likely to survive.

Interdependence and Changes

• All species in a food chain or web depend on each other.

• If one species decreases or dies out, it can affect many others.

• Example: If grass dies, rabbits will starve, and foxes that eat rabbits will also decrease.

Predator and Prey

• Predator: Hunts and eats other animals.

• Prey: The animal that is eaten.

• Prey animals have adaptations like camouflage or toxins to protect themselves.

Predator-Prey Cycles

• Predator and prey populations rise and fall in cycles.

• Example: More rabbits → more foxes. Fewer rabbits → fewer foxes later.

• These cycles affect the entire food web.