D3-D4 Revision Guide: Continuity and Change: Organisms & Ecosystems

Sexual Reproduction

Involves two parents; offspring are genetically diverse.

Asexual Reproduction

Involves one parent; offspring are genetically identical to the parent.

Meiosis

A process that shuffles genes through independent assortment and crossing over, producing genetically unique gametes.

Males

Produce sperm in testes; generally smaller gametes compared to females.

Females

Produce eggs in ovaries; generally larger gametes and provide more parental investment.

FSH and LH

Hormones that stimulate ovulation; work alongside estrogen and progesterone which regulate the lining of the uterus.

Fertilization

The process where sperm meets egg in the fallopian tube leading to the formation of a zygote.

Genotype

The genetic makeup of an organism (e.g., Bb).

Phenotype

The observable traits of an organism (e.g., brown eyes).

Dominant Allele

An allele that masks the effect of a recessive allele.

Recessive Allele

An allele only expressed when both alleles are recessive.

Phenylketonuria (PKU)

A genetic disorder that prevents the breakdown of phenylalanine, potentially causing brain damage if untreated.

Incomplete Dominance

A genetic situation in which one allele does not completely dominate another, resulting in a third phenotype (e.g., red + white = pink).

Codominance

A situation in which both alleles contribute to the phenotype (e.g., AB blood type).

Haemophilia

An X-linked recessive disorder that mainly affects males due to having only one X chromosome.

Pedigree Chart

A diagram that illustrates the genetic relationships within a family, used to trace inheritance patterns.

Homeostasis

The maintenance of stable internal conditions in an organism.

Negative Feedback

A process that counteracts a change to restore stability (e.g., sweating cools the body down).

Diabetes Type 1

A condition where the body does not produce insulin.

Diabetes Type 2

A condition referred to as insulin resistance, where the body's cells do not respond effectively to insulin.

Natural Selection

The process where organisms better adapted to their environment tend to survive and produce more offspring.

Keystone Species

Species that have a disproportionately large effect on their environment relative to their abundance.

Anthropogenic Climate Change

Climate change that is caused by human activities such as burning fossil fuels and deforestation.

Carbon Sequestration

The process of capturing and storing atmospheric carbon dioxide to mitigate climate change.

Eutrophication

The process where excess nutrients lead to algal blooms, resulting in oxygen depletion in water bodies.

Sustainable Agriculture

Farming practices that maintain the health of the environment and the resources over the long term.