Inheritance, Evolution, and Variation

This section delves into the mechanisms of reproduction, genetics, and evolution. It begins by contrasting asexual and sexual reproduction. Mitosis is explained as the process for growth and tissue repair, while meiosis produces gametes for sexual reproduction.

Definition: Fertilization is the fusion of the nucleus of a male gamete with the nucleus of a female gamete.

Key genetic concepts are introduced, including genes, genomes, chromosomes, and alleles. The differences between dominant and recessive alleles are explained. The section also covers genetic disorders like cystic fibrosis and polydactyly, as well as the use of genetic testing.

Example: Cystic fibrosis affects the lungs, causing the production of sticky mucus.

The concept of variation - differences between individuals - is explored, along with mutations as a source of genetic change. Natural selection is introduced as a mechanism for evolution, where organisms better adapted to their environment are more likely to survive and reproduce.

Highlight: How does natural selection lead to evolution? Organisms with advantageous traits are more likely to survive and pass on their genes, gradually changing the population over time.

Selective breeding and genetic modification $GM$ are discussed as human interventions in genetics, with both pros and cons outlined. The section concludes by mentioning evidence for evolution, including the fossil record and extinction events.

Vocabulary: Genetic modification $GM$ involves altering an organism's genome by introducing genes from another organism.

Homeostasis and Response

This section focuses on how organisms maintain internal balance and respond to environmental changes. Homeostasis is introduced as the maintenance of optimal conditions for enzyme action throughout the body.

Definition: Homeostasis is the maintenance of a stable internal environment within an organism, despite changes in the external environment.

The nervous system is outlined, including the central nervous system $CNS$ comprising the brain and spinal cord. The roles of receptors, neurons, and effectors in detecting and responding to stimuli are explained. The concept of reflex actions and the reflex arc is introduced.

Example: A reflex action could be automatically pulling your hand away from a hot surface before you consciously feel the pain.

The endocrine system and its use of hormones for regulation are discussed. Specific hormones like thyroxine, adrenaline, and insulin are explained along with their functions and regulatory mechanisms.

Highlight: Insulin, produced by the pancreas, regulates blood glucose levels. Its absence or ineffectiveness leads to diabetes.

The section covers both Type 1 and Type 2 diabetes, explaining their causes and treatments. Puberty and the roles of sex hormones $testosterone and estrogen$ in developing secondary sexual characteristics are discussed. The female menstrual cycle and its hormonal control are outlined.

Vocabulary: Puberty is the period during which a child's body develops into an adult body capable of sexual reproduction.

The document concludes by summarizing the coordination of responses in the body, emphasizing the roles of the nervous and endocrine systems in maintaining homeostasis and responding to environmental changes.

Quote: "Nervous system: stimulus - receptor - coordinator - effector - response."

Genetic Concepts and Variations

This page delves deeper into genetic concepts, variations, and their applications. It begins by explaining that sperm and egg cells are haploid, meaning they contain half the number of chromosomes compared to other body cells.

The process of meiosis is mentioned as the method by which these cells divide. The page then provides examples of genetic conditions:

Example: Cystic fibrosis, which affects the lungs by producing sticky mucus, and polydactyly, a condition resulting in extra fingers or toes.

Genetic testing is introduced as the analysis of a person's DNA. The page then explores the concept of variations, defining them as differences between individuals.

Definition: A mutation is a change in a gene or chromosome.

The process of natural selection is explained, emphasizing that organisms better adapted to an environment are more likely to survive and reproduce.

Selective breeding is described as the process of breeding organisms with desired characteristics. The page then introduces genetic modification $GM$:

Vocabulary: Genetic Modification $GM$ involves modifying the genome of an organism by introducing a gene from another organism.

Pros and cons of GM are discussed:

• Pros: herbicide resistance and improved crop yields
• Cons: ethical concerns and potential harm from GM crops

The page concludes by touching on the concept of evolution, stating that all living things have evolved over time. Evidence for evolution, such as the existence of extinct species, is briefly mentioned.

Homeostasis and Response Systems

This page introduces the concept of homeostasis and the body's response systems. Homeostasis is defined as the maintenance of optimal conditions for enzyme action throughout the body.

The nervous system is described, with a focus on the Central Nervous System $CNS$ comprising the brain and spinal cord. Key components of the nervous system are explained:

Vocabulary:

• Receptors: detect stimuli $changes in the environment$
• Neurones: nerve cells with long fibers to carry messages up and down the body
• Effectors: produce a specific response to a detected stimulus

The page introduces the concept of reflex actions, describing them as automatic and rapid responses to stimuli. The nerve pathway followed by a reflex action is called a reflex arc.

Example: A reflex arc could be triggered by accidentally touching something hot, causing an immediate withdrawal response.

The synapse, a small gap where two neurones meet, is mentioned. The page then transitions to discussing hormones:

Definition: A hormone is a chemical substance produced by a gland and carried in the bloodstream.

This introduction to homeostasis and response systems provides a foundation for understanding how the body maintains balance and reacts to environmental changes.

Hormones and Homeostasis

This page delves deeper into the role of hormones in maintaining homeostasis, with a focus on specific hormones and their functions. It begins by discussing thyroxine, a hormone produced by the thyroid gland that stimulates the basal metabolic rate.

The feedback mechanism for thyroxine regulation is explained:

Example: When thyroxine levels are low, the hypothalamus is stimulated to release TRH, which causes the pituitary gland to release TSH. This, in turn, prompts the thyroid to release more thyroxine, bringing blood levels back to normal.

The hormone adrenaline, produced by the adrenal glands in response to fear or stress, is briefly mentioned.

The page then focuses on glucose regulation and diabetes:

Highlight: Glucose is needed by cells for respiration. Insulin, produced by the pancreas, regulates glucose concentrations in the blood.

Diabetes is explained as a condition where blood glucose is too high. The page describes how diabetes is treated by injecting insulin, which causes the liver to convert glucose into glycogen, reducing blood sugar levels.

Two types of diabetes are distinguished:

1. Type 1 diabetes: The pancreas fails to produce enough insulin.
2. Type 2 diabetes: The person's body cells do not respond properly to insulin produced by the pancreas.

The page emphasizes the importance of monitoring blood sugar levels for individuals with diabetes.

Hormones and Reproductive System

This page focuses on hormones related to puberty and the reproductive system. It begins by defining puberty as the period when a child's body develops into an adult's.

Key hormones and their functions are explained:

Vocabulary:

• Testosterone: Produced by testes, controls development of male secondary characteristics
• Estrogen: Produced by ovaries, controls development of female secondary characteristics

The page reiterates that a hormone is a chemical substance.

The female reproductive cycle is described:

Highlight: In females, eggs mature and one is released every 28 days after puberty. This process is known as the menstrual cycle.

Two important hormones in the female reproductive cycle are introduced:

1. FSH $Follicle Stimulating Hormone$: Responsible for the maturation of eggs in the ovary
2. LH $Luteinizing Hormone$: Stimulates the release of the egg

This information provides a foundation for understanding the hormonal regulation of the reproductive system and the changes that occur during puberty.

Coordination and Response Systems

This final page summarizes key concepts related to coordination and response systems in the body. It begins by mentioning contraceptives, though no further details are provided.

The role of coordination centers is explained:

Definition: Coordination centers obtain and process information from receptors.

The nervous system is described as allowing the body to react and make appropriate responses to stimuli. The general pathway of the nervous system is outlined:

stimulus → receptor → coordinator → effector → response

The page revisits two important hormones and their functions:

1. Adrenaline: Associated with the "fight or flight" response
2. Thyroxine: Affects metabolic rate and is produced in the thyroid gland

This summary reinforces the interconnected nature of the body's coordination and response systems, highlighting how various components work together to maintain homeostasis and react to environmental changes.

Ecology and Ecosystems

This section introduces key ecological concepts and interactions within ecosystems. An ecosystem comprises all the living organisms in a particular area, forming a community of two or more interacting populations. The food chain is explained, from producers like plants to various levels of consumers.

Definition: An ecosystem is all the living organisms in a particular area and their interactions with each other and the environment.

The interdependence of organisms in an ecosystem is emphasized, along with the roles of abiotic $non-living$ and biotic $living$ factors. Competition among animals for resources like food, mates and territory is discussed. Plant and animal adaptations, both structural and behavioral, are explained as ways organisms gain advantages in their environment.

Example: Structural adaptations in animals could include camouflage coloration, while behavioral adaptations might involve migration patterns.

The concept of extremophiles - organisms living in extreme environments - is introduced. The roles of predators and prey in ecosystems are outlined. The important function of decomposing bacteria and fungi in recycling nutrients is highlighted.

Highlight: How do decomposing bacteria recycle nutrients in ecosystems? They break down dead organisms, releasing nutrients back into the environment for use by other organisms.

Key ecological cycles like the carbon cycle and water cycle are mentioned. The document also touches on biodiversity and human impacts on ecosystems through population growth, pollution, and deforestation.

Vocabulary: Biodiversity refers to the variety of plant and animal life in a particular habitat or ecosystem.