Ecosystems

• An ecosystem includes all the living (biotic) and nonliving (abiotic) components in a particular area and how they interact.

• Ecosystems can be small (like a pond) or large (like a rainforest).

• Ecosystems are dynamic, meaning they change over time due to natural events (like storms) or human activity (like deforestation).

• Biodiversity in ecosystems contributes to stability and resilience, helping ecosystems recover from disturbances.

Biotic Factors

• Biotic factors are the living components of an ecosystem.

• Examples: plants, animals, fungi, bacteria, and any other living organisms.

• Biotic factors interact with each other through relationships like:

• Predation (one organism eats another)

• Competition (organisms compete for resources)

Abiotic Factors

• Abiotic factors are the nonliving components of an ecosystem.

• Examples: sunlight, water, temperature, soil, air, nutrients, and rocks.

• Abiotic factors limit the types and numbers of organisms that can live in an ecosystem.

• Changes in abiotic factors can cause major shifts in an ecosystem (e.g., drought, temperature changes).

Energy Flow in Ecosystems

• Energy enters ecosystems from the Sun, captured by producers (plants and algae) through photosynthesis.

• Producers → Consumers → Decomposers: Energy flows in one direction through trophic levels:

  • Producers – make their own food (plants, algae)

  • Primary consumers – herbivores (eat plants)

  • Secondary consumers – carnivores or omnivores (eat herbivores)

  • Tertiary consumers – top predators

  • Decomposers – break down dead organisms, recycling nutrients back into the ecosystem

⭐Only about 10% of energy moves from one trophic level to the next; most energy is lost as heat.

1. Definition

• Biodiversity is the variety of life in a particular habitat or ecosystem.
      Includes diversity within species, between species, and of ecosystems.

2. Types of Biodiversity

• Genetic diversity – variation in genes within a species (e.g., different breeds of dogs).

• Species diversity – the number of different species in an ecosystem.

• Ecosystem diversity – variety of ecosystems (e.g., forests, deserts, wetlands).

3. Importance of Biodiversity

• Ecosystem stability – diverse ecosystems are more resilient to changes like disease or natural disasters.

• Food and resources – provides plants, animals, and materials humans rely on.

• Medicine and science – many drugs and treatments come from plant and animal species.

• Environmental services – clean air, water, pollination, nutrient cycling.

• Cultural and recreational value – nature contributes to human well-being and tourism.

4. Threats to Biodiversity

• Habitat destruction (deforestation, urbanization)

• Pollution (air, water, soil)

• Climate change

• Overhunting and overfishing

• Invasive species (non-native species that disrupt ecosystems)

5. Conservation

• Protected areas (national parks, wildlife reserves)

• Sustainable practices (fishing quotas, responsible farming)

• Restoration of habitats

• Captive breeding and reintroduction programs

Ecological Succession

• Ecological succession is the gradual process by which ecosystems change and develop over time.

• It results in changes in species composition, structure, and biodiversity.

• There are two main types: primary and secondary succession.

Primary Succession

• Occurs in areas where no soil exists (bare rock, lava flows, or areas left by glaciers).

• Pioneer species, like lichens and mosses, are the first to colonize.

• Over time, soil forms from weathered rock and decomposing organisms.

• Gradually, larger plants (grasses, shrubs, trees) can grow, leading to a mature, stable ecosystem called a climax community.

• Example: the formation of a forest on bare volcanic rock.
  
  

Secondary Succession

• Occurs in areas where a community has been disturbed, but soil is already present.

• Happens after events like forest fires, floods, farming, or logging.

• Weedy and fast-growing plants often appear first.

• Over time, shrubs and trees return, and the ecosystem gradually restores toward a climax community.
  Example: regrowth of a forest after a fire.

Cells

• Cells are the basic unit of life; all living things are made of cells.

• There are two main types of eukaryotic cells: plant cells and animal cells.

• Both plant and animal cells have organelles, which are specialized structures that perform specific functions.

Organelles in Both Plant and Animal Cells

Organelle                                                         Function                                                    

Nucleus                                  Controls cell activities; contains DNA

Mitochondria Produces energy (ATP) through cellular respiration

Ribosomes Make proteins

Golgi apparatus Processes and packages proteins and lipids

Cytoplasm Jelly-like fluid where organelles are suspended

Cell membrane Controls what enters and leaves the cell

Vacuole Stores water, nutrients, and waste (small in animal cells, large in plant cells)

Organelles Only In Plant Cells

Organelle Function

Cell wall                                      Provides structure and protection; made of cellulose

Chloroplasts                               Conduct photosynthesis to make food (glucose)

Large central vacuole                 Stores water and maintains cell rigidity (turgor pressure)

Organelles Only In Animal Cells

Organelle Function

Lysosomes Break down waste, old cell parts, and foreign invaders

Key Differences Between Plant and Animal Cells

• Plant cells have a cell wall, chloroplasts, and large central vacuole.

• Animal cells do not have a cell wall or chloroplasts and have smaller vacuoles.

⭐⭐⭐⭐⭐Both cell types share the nucleus, mitochondria, ribosomes, Golgi apparatus, and cytoplasm. ⭐⭐⭐⭐⭐

Genetics

• Genetics is the study of how traits are passed from parents to offspring.

• Traits are controlled by genes, which are segments of DNA.

• Each organism has a genotype (genetic makeup) and a phenotype (observable traits).

Alleles

• Alleles are different versions of a gene.

• Organisms inherit two alleles for each gene—one from each parent.

• Types of alleles:

  • Dominant allele (capital letter): masks the effect of a recessive allele (e.g., B)

  • Recessive allele (lowercase letter): expressed only if both alleles are recessive (e.g., b)

Genotypes

• Homozygous: both alleles are the same (BB or bb)

• Heterozygous: alleles are different (Bb)

Phenotypes

• Phenotype is the physical expression of a genotype.

• Example:

  • Genotype BB → Phenotype: brown eyes

  • Genotype bb → Phenotype: blue eyes

  • Genotype Bb → Phenotype: brown eyes (dominant trait shows)

Trait Variations

• Inherited traits: traits passed from parents to offspring (e.g., eye color, hair color)

• Acquired traits: traits gained during an organism’s life (e.g., scars, learned skills)

• Genetic variation occurs due to:

  • Mutations – random changes in DNA

  • Sexual reproduction – mixing of alleles from two parents

Key Points

• Variation is important for populations—it allows adaptation and survival in changing environments.

• Traits can be simple (controlled by one gene) or complex (controlled by multiple genes and influenced by the environment).

Adaptations

• Adaptations are traits that help organisms survive and reproduce in their environment.

• Types of adaptations:

  1. 1. 1. Structural adaptations – physical features (e.g., thick fur, long necks, sharp teeth)

        2. Behavioral adaptations – actions or behaviors (e.g., migration, hibernation, hunting in packs)

        3. Physiological  adaptations – internal body processes (e.g., producing venom, storing water)

• Adaptations develop over many generations through genetic variation and environmental pressures.

Natural Selection

• Natural selection is the process by which organisms with advantageous traits survive and reproduce more successfully.

• Key steps in natural selection:

  1. 1. 1. Variation exists within a population.

        2. Competition occurs for limited resources.

        3. Differential survival and reproduction – individuals with helpful traits are more likely to survive and pass on those traits.

        4. Change in population over time – the frequency of beneficial traits increases.

• “Survival of the fittest” means the best-adapted individuals leave more offspring, not necessarily the strongest.
  
  

Key Points

• Adaptations increase the chances of survival in a particular environment.

• Natural selection drives evolution, shaping populations over generations.

• Environments can change, so adaptations that are advantageous in one situation might be disadvantageous in another.

• Genetic variation is essential for natural selection to occur.