Life Science Notes

Parasitism

  • Parasitism is a symbiotic relationship where one party (the parasite) benefits while the other (the host) is disadvantaged.

Producers and Consumers

  • Producers: Plants that produce their own food through photosynthesis; also called autotrophs.

  • Consumers: Organisms that obtain food directly or indirectly from plants.

    • Consume other organisms.

    • Require carbon dioxide, light, water, and produce carbohydrates and oxygen.

Herbivores and Carnivores

  • Herbivores: Primary consumers that feed only on plants.

  • Carnivores: Meat eaters; can be secondary or tertiary consumers.

    • Examples:

    • Tertiary Consumers: Fox and Hawk

    • Secondary Consumers: Frog and Snake

    • Primary Consumers: Grasshopper and Squirrel

    • Producers: Plants

    • Decomposers: Worms

Predators and Scavengers

  • Predators: Carnivores that hunt and kill for food. The hunted animals are known as prey.

  • Scavengers: Carnivores that feed on animals already dead.

Insectivores and Omnivores

  • Insectivores: Animals that mainly feed on insects and other smaller invertebrates.

  • Omnivores: Animals whose diet consists of both plants and meat.

Detritivores and Decomposers

  • Detritivores: Scavengers that feed on waste/detritus of plants and animals, enlarging the contact surface for decomposers.

  • Decomposers: Microorganisms (bacteria and fungi) that decompose (break down) the remains of dead plant and animal material.

Energy Flow and Balance in Ecosystems

  • Energy flow starts with producers and ends with decomposers.

  • Arrows in food chains indicate the direction of energy flow.

Food Chain

  • A sequence showing the transfer of energy from one organism to another.

    • Example: Grass (producer) → Grasshopper (primary consumer) → Frog (secondary consumer) → Snake (tertiary consumer) → Hawk (final consumer) → Fungi (decomposer).

Food Web

  • A variety of interlinked food chains.

    • Examples: plants being consumed by grasshoppers and ground squirrels, which are in turn preyed upon by birds, eagles, and foxes.

Trophic Levels (Feeding Levels)

  • Level 1: Plants (producers).

  • Level 2: Primary consumers (herbivores).

  • Level 3: Secondary consumers (carnivores).

  • Level 4: Tertiary consumers (top carnivores).

Energy Pyramids

  • Represents the numbers and flow of energy from organisms on one trophic level to the next.

  • Energy and numbers of organisms decrease at higher trophic levels.

  • Organisms use energy for respiration, reproduction, and excretion, making survival possible.

  • Approximately 10% of the net energy production of one trophic level is transferred to the next.

  • Less energy is available for the next trophic level.

Energy Transfer in Ecosystems

  • Approximately 10% of energy consumed at one trophic level is available to the next.

  • Energy is used for respiration, heat loss, reproduction, and egestion (solid waste) and excretion (urine).

Trophic Levels Visualized (Marine Example)

  • Level 6: Top Carnivores (e.g., shark, dolphin, albatross) - 10J

  • Level 5: 3rd Level Carnivorous Consumers (e.g., squid) - 100J transferred from below.

  • Level 4: 2nd Level Carnivorous Consumers (e.g., larger fish) -1,000J transferred from below.

  • Level 3: 1st Level Carnivorous Consumers (e.g., juvenile stages of fish and jellyfish, small fish, crustaceans, and sea stars) - 10,000J transferred from below.

  • Level 2: Herbivorous Consumers (e.g., zooplankton, cockles) - 100,000J transferred from below.

  • Level 1: Primary Producers (e.g., phytoplankton, seaweed) - 1,000,000J of sunlight. Decomposers also exist at all levels.

Ecological Balance

  • An ecosystem can only accommodate as many organisms as its resources (food, water, shelter) can sustain.

  • Imbalance between resources and organisms can detrimentally influence the ecosystem.

  • Ecological balance is a stable balance in the number of each species in an ecosystem.

Factors Influencing Ecosystem Balance

  • Natural Factors:

    • Food shortages

    • Predators

    • Diseases

    • Droughts/floods

    • Populations usually survive imbalances caused by natural factors.

  • Human Factors:

    • Habitat destruction

    • Pollution

    • Climate change

    • Populations may not survive imbalances caused by human factors and may become extinct.

    • Examples: Kwagga, Javan Tiger, Golden Frog

Photosynthesis

  • Plants absorb radiant energy from the sun to produce glucose from water and carbon dioxide.

  • Oxygen is a by-product.

  • Energy in glucose is chemical potential energy.

  • Plants use glucose for metabolic processes (growth), to make cellulose (fiber in the cell wall), and store extra energy as starch.

  • Photosynthesis is a chemical reaction.

  • Balanced equation: 6CO2 + 6H2O \xrightarrow{Energy, Enzymes} C6H{12}O6 + 6O2

Plant Cell Structure and Photosynthesis

  • Cell wall provides support and structure.

  • Chloroplasts contain chlorophyll (green pigment) and are only in plant cells.

  • Key components:

    • Cytoplasm

    • Nucleus

    • Cell membrane

    • Cellulose cell wall

    • Mitochondrion

    • Permanent vacuole

    • Chloroplast

Biological Importance of Photosynthesis

  • Food production and full answer food

Leaves of a Plant

  • Leaves are the main organ responsible for photosynthesis.

  • Key structures (transverse section):

    • Lamina

    • Midrib

    • Margin

    • Vein

  • Cell types from top to bottom:

    • Cuticle

    • Upper epidermis

    • Mesophyll layer (palisade and spongy)

    • Vascular bundle (xylem and pholem)

    • Lower epidermis (containing stomata and guard cells

  • Diagram must include:

    • Cell wall

    • Vacuole

    • Cytoplasm

    • Nucleus

    • Chloroplast

    • Air space

Chloroplast Structure

  • Two envelope membranes (inner and outer) with an intermediate space.

  • Grana: Stacks of thylakoids.

  • Stroma: Dense fluid inside the chloroplast.

  • Thylakoids contain chlorophyll.

  • Diagram Label:

    • Outer membrane

    • Inner membrane

    • Thylakoid

    • Lamella

    • Grana

    • Stroma

Testing for Starch in a Leaf

  • Positive starch test indicates photosynthesis has occurred.

    Procedure:

    1. Place the leaf in boiling water for 30 seconds to kill it, stopping chemical reactions.

    2. Place the leaf in boiling ethanol to remove chlorophyll, making color changes more visible. (Heat alcohol in a water bath to avoid naked flame).

    3. Dip the leaf again in water to soften it.

    4. Spread the leaf on a white tile and add iodine solution to test for starch.

    Results:

    • If starch is present, iodine changes from yellow-brown to blue-black.

    • If starch is absent, iodine remains yellow-brown.

    Safety:

    • Wear goggles.

    • Avoid naked flame near ethanol; use a water bath.

    De-starching a Plant:

    • Place the plant in the dark for at least 48 hours to remove or use any starch.

    Control:

    • Control, used as a standard or for comparison, will remain unchanged or unaffected.

The Scientific Method

Steps:

  1. Investigative question.

  2. Formulate a hypothesis.

  3. Identify all variables.

  4. Method: Do the investigation.

  5. Make observations.

  6. Record results (e.g., in a table) and interpret results (e.g., drawing a graph).

  7. Make a conclusion.

Investigative Questions

  • A question about something observed that is unknown or unclear.

*Example: Will temperature change smoothly when heated over a constant heat source?

Variables

  1. Independent (manipulated) variable:

    • The factor you deliberately change or set during the experiment.

Only one factor should be manipulated at a time to clearly identify the cause of change in the responding variable. For example only sunlight on plant growth, not more than one

  1. Dependent (responding) variable:

    • The factor that is monitored or measured during the experiment to see how it is affected when the independent variable changes.

  2. Fixed (controlled) variables:

    • Other factors that may affect the experiment and need to be kept constant.

Conditions such as using the same thermometer and heat source.

Hypothesis

  • An informed prediction of what the result will be (a statement).

*Identify your independent variable.

*Identify your dependent variable.

Using the rule when you make your hypothesis: If (refer to the independent variable), then (refer to the dependent variable).

Example: If the duration of heating increases, then the temperature of the water increases.

Types of Observations

  • Quantitative Observations: Use numbers (e.g., measuring temperature).

  • Qualitative Observations: Describe what you see; do not involve numbers (e.g., noting that a ball is round).

Recording of Results

  • Results are recorded in a suitable table.

Graphs

  • Graphs presents results as a picture, which is very helpful

*It helps us to see the realtionshipp in data.

  • Must have a heading describing the data.

  • The x-axis (independent variable) and y-axis (dependent variable) must be labelled with appropriate units.

  • Both axes must be scaled appropriately.

Conclusion

  • Answer the investigative question and state whether to accept or reject the hypothesis.

  • Follow the "if" - "then" - rule.

*Example: IF water at a very low temperature, is heated, THEN the temperature of the water will increase. I accept my hypothesis.

Respiration

  • Photosynthesis is the first stage of energy flow through an ecosystem.

  • Plants and animals burn energy.

  • Respiration releases stored energy for use and occurs in the mitochondria inside each cell.

  • Chemically, respiration is photosynthesis in reverse: C6H{12}O6 + 6O2 \rightarrow 6H2O + 6CO2 + energy

  • Respiration occurs in cells and is fuelled by oxygen.

  • The carbon dioxide exhaled is the result of cellular respiration.

  • Only plants photosynthesize, but both plants and animals depend on respiration to release the chemical potential energy originally captured through photosynthesis.

Mitochondria

  • Membrane-bound organelle in cytoplasm of eukaryotic cells.

  • Each cell can have one to thousands of mitochondria.

  • Called the powerhouse of the cell.

  • Function: A catabolic process where a large molecule is broken into smaller molecules.

  • Biological diagram includes:

    • Outer Mitochondrial Membrane

    • Inner Mitochondrial Membrane

    • Space between Inner and Outer Membranes

    • Cristae

    • Matrix

    • 70S Ribosomes

Internal folds form cristae to increase surface area and maximize cellular respiration rate.

Types of Respiration

  1. Aerobic Respiration:

    • Requires oxygen for effective respiration in people, plants, and animals.

    • Requirements: glucose and oxygen.

    • Products: energy, carbon dioxide, and water.

  2. Anaerobic Respiration:

    • Occurs when oxygen supply is insufficient.

    • In animals, lactic acid forms as an intermediate product, causing muscle stiffness.

    • In plants, plant cells form alcohol and carbon dioxide, used in the wine making industry.

    • Yeast cells and bacteria can only undergo anaerobic respiration to get energy from breaking down glucose without oxygen.

    • Products: energy, ethanol, and carbon dioxide.

Ecology

  • The study of interactions of organisms with one another and with the physical and chemical environment.

Ecosystem

  • An area consisting of an ecological community where living (biotic) and non-living (abiotic) factors exist and interact.

    • biotic example plants, Protozoane and insects

    • abiotic example sunlight, termite mounds.

Other Ecological Concepts

  • Biosphere: The sum total of all the ecosystems on earth; encompasses lithosphere, atmosphere, and hydrosphere.

  • Biodiversity: The variety of life that occurs in one ecosystem/habitat.

Ecological Components

  • Habitat: The natural home or environment of a plant, animal, or other organism.

  • Community: All the populations living in an area.

Population and Species

  • Population: All the organisms of the same species living in an area.

  • Species: A group of individuals that can interbreed and produce fertile offspring.

    • Example: Horses and donkeys are not the same species because their offspring (mules) are sterile.

Abiotic and Biotic Factors

  • Abiotic factor: The non-living parts of an ecosystem.

    • Examples: water, minerals, temperature

  • Biotic factor: The living parts of an ecosystem.

    • Examples: animals, plants, fungi, protists

Levels of Organization

  • Biosphere consists of Ecosystems, which consist of