Genetics, Ecology, and Food Chains: A Comprehensive Guide
Haploid Nucleus
23 chromosomes
Diploid Nucleus
46 chromosomes
Genotype
Examples: Tt, Bb, Rr
Phenotype
Example: A tall plant or a dwarf plant
Homozygous
Example: TT
Heterozygous
Example: Tt
Dominant Allele
Represented by a capital letter
Recessive Allele
Represented by a small letter
Mitosis
Mitosis is a nuclear division that produces genetically identical cells. The chromosome number is maintained by the exact duplication of chromosomes. Mitosis occurs when an organism is growing, repairing a damaged part of its body, or replacing worn-out cells. It is a form of asexual reproduction.
Meiosis
Meiosis is a reduction division in which the chromosome number is halved from diploid to haploid. It introduces genetic variation.
Mutation
A mutation is an unpredictable change in genes or chromosome number. It can occur due to:
- Errors during DNA replication
- Faulty separation of chromosomes during cell division
- Exposure to radiation or certain chemicals
Down’s Syndrome
Down’s syndrome is caused by a mutation that occurs when ova are formed in the ovaries, resulting in an extra copy of chromosome 21.
Sickle Cell Anemia
Sickle cell anemia is caused by a mutation in the gene for the blood pigment hemoglobin. This faulty hemoglobin causes red blood cells to deform into a sickle shape, especially when oxygen levels are low.
Genetic Engineering
Genetic engineering is the process of transferring a gene from one species to another.
Process of Inserting the Human Insulin Gene into a Bacterial Cell
- Human cells containing the gene for healthy insulin are selected.
- A chromosome (a length of DNA) is removed from the cell.
- The insulin gene is cut from the chromosome using a restriction endonuclease enzyme.
- A suitable bacterial cell is selected. Some of its DNA is in the form of circular plasmids.
- All the plasmids are removed from the bacterial cell.
- The plasmids are cut open using the same restriction endonuclease enzyme.
- The human insulin gene is inserted into the plasmids using ligase enzyme.
- The plasmid is returned to the bacterial cell.
- The bacterial cell is allowed to reproduce in a fermenter. All the cells produced contain plasmids with the human insulin gene.
Species
A group of organisms that can interbreed and produce fertile offspring.
Habitat
The type of environment in which an organism or group normally lives.
Population
A group of organisms of the same species that live in the same area at the same time.
Community
A group of interdependent organisms inhabiting the same region and interacting with each other.
Ecosystem
A community of organisms and their abiotic environment.
Ecology
The study of relationships between living organisms and between organisms and their environment.
Trophic Level
The feeding level in a food web defined by the number of energy transfers away from the original source of energy.
Autotroph
An organism that synthesizes its organic molecules from simple inorganic substances (e.g., plants).
Heterotroph
An organism that obtains organic molecules from other organisms (e.g., animals).
Consumer
An organism that ingests other organic matter that is living or recently killed.
Detritivore
An organism that ingests non-living organic matter.
Saprotroph
An organism that lives on or in non-living organic matter, secreting digestive enzymes and absorbing digested products (e.g., fungi).
Food Chain
A series of steps in which organisms transfer energy by eating and being eaten.
Food Web
A complex arrangement of interrelated food chains illustrating the flow of energy between interdependent organisms.
Food Pyramid
A graphical representation of the relative sizes of different components at the various trophic levels of a food chain. There are three types of ecological pyramids: numbers, biomass, and energy.
Energy Flow in Ecosystems
The sun is the main source of energy for most ecosystems. Photosynthetic plants and some bacteria can trap light energy and convert it into chemical energy. Energy is lost as heat through respiration and movement.
Energy flow in a food chain:
Producers (plants) → Primary consumers (herbivores) → Secondary consumers (small carnivores) → Tertiary consumers (larger carnivores)
About 90% of the energy is lost at each trophic level in a food chain.
Food Chain Examples
- Mahogany tree → Caterpillar → Songbird → Hawk
- Maize → Locust → Lizard → Snake
Factors Affecting Food Web Balance
- Over-predation or hunting
- Disease
- Pollution
- Use of pesticides
- Lack of food (or other resources)
- Emigration
Pyramid of Numbers
A pyramid of numbers shows the relative number of organisms at each stage of a food chain.
Pyramid of Energy
A pyramid of energy shows the amount of energy trapped per unit time and area at each stage of a food chain.
Carbon Cycle
Main processes of the carbon cycle:
- Photosynthesis
- Respiration
- Decomposition
- Combustion
Human activities affecting the carbon cycle:
- Cutting down forests (deforestation) – reduces photosynthesis
- Combustion of fossil fuels (coal, oil, and gas) – releases carbon dioxide into the atmosphere
- Increasing numbers of animals (including humans) – increases respiration, releasing carbon dioxide