DNA Structure and Function

This page details the structure of DNA, crucial for homeostasis biology higher unit 2 notes GCSE:

• Double helix structure composed of sugar-phosphate backbone and complementary base pairs
• Nucleotide bases: Adenine $A$, Thymine $T$, Guanine $G$, and Cytosine $C$
• A-T and G-C base pairing
• Applications of DNA analysis: Genetic profiling Paternity and maternity testing Ethnicity determination Criminal investigations Organism classification

Definition: DNA $Deoxyribonucleic Acid$ is the molecule that carries genetic instructions for development, functioning, growth, and reproduction of all known organisms.

Highlight: Understanding DNA structure is fundamental to grasping concepts in genetics and inheritance, key topics in WJEC GCSE Biology Unit 2 revision.

Lymphocytes and Immune Response

This page focuses on lymphocytes, a crucial component of the immune system relevant to homeostasis and response notes:

• Lymphocytes are a type of white blood cell
• They recognize pathogens by their antigens
• Upon recognition, lymphocytes produce specific antibodies
• Antibodies bind to antigens on pathogens to neutralize or destroy them

Vocabulary: Antigen - A substance that triggers an immune response, typically foreign proteins on pathogens

Example: When a virus enters the body, lymphocytes produce antibodies specifically designed to bind to that virus's antigens, marking it for destruction.

Phagocytes in Immune Defense

This page explains the role of phagocytes in the immune system, an important topic for homeostasis GCSE exam questions PDF:

• Phagocytes are a type of white blood cell
• They recognize invading bacteria as foreign
• The phagocyte engulfs the bacterium in a process called phagocytosis
• Enzymes within the phagocyte then digest and destroy the engulfed bacterium

Definition: Phagocytosis is the process by which certain cells, called phagocytes, engulf and destroy foreign particles, bacteria, and cell debris.

Highlight: Phagocytes form a crucial part of the body's innate immune system, providing a first line of defense against many pathogens.

Homeostasis: Maintaining Body Balance

This page introduces the concept of homeostasis, central to homeostasis biology higher unit 2 notes:

• Homeostasis is the maintenance of constant internal conditions in the body
• It prevents harmful effects from environmental changes
• Temperature regulation is a key example of homeostasis: When too cold: hairs stand up, blood supply to skin decreases $vasoconstriction$, no sweating When too hot: hairs lie flat, increased sweating, blood supply to skin increases $vasodilation$

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

Example: When body temperature rises, sweat glands activate to cool the body down, demonstrating a homeostatic response.

Skin Structure and Thermoregulation

This page details skin structure and its role in temperature regulation, important for homeostasis and response notes:

• Components of skin structure: Hair and erector muscles Nerves Fat and oil glands Pores Capillaries Sweat ducts and glands

Highlight: The skin's complex structure allows it to play a crucial role in thermoregulation, a key homeostatic process.

Vocabulary: Erector muscles - Small muscles attached to hair follicles that cause hair to stand up in response to cold.

The Nervous System and Reflexes

This page covers the nervous system and reflexes, essential topics in homeostasis biology notes PDF:

• Sense organs and their functions: Eyes: Identify changes in light Tongue: Detect chemicals $taste$ Nose: Detect chemicals $smell$ Ears: Detect vibrations and changes in position Skin: Detect changes in temperature and pressure
• Components of the nervous system: Central nervous system: Brain and spinal cord Peripheral nervous system: Nerves throughout the body

Definition: The nervous system is the body's electrical wiring that transmits signals between different parts of the body.

Highlight: Understanding the nervous system is crucial for answering GCSE Biology homeostasis and response exam questions.

Reflex Arc Structure

This page illustrates the structure of a reflex arc, a key concept in homeostasis biology higher unit 2 notes GCSE:

• Components of a reflex arc: Receptor: Detects the stimulus Sensory neurone: Carries signal to spinal cord Relay neurone: In the spinal cord, connects sensory and motor neurones Motor neurone: Carries signal from spinal cord to effector Effector: Muscle or gland that responds to the stimulus

Example: When you touch a hot object, a reflex arc quickly signals your hand to pull away before the conscious part of your brain processes the heat.

Highlight: Reflex arcs allow for rapid, automatic responses to stimuli, bypassing the slower conscious decision-making process.

Pathogens and Body Defenses

This page discusses pathogens and the body's defense mechanisms, relevant to homeostasis and response notes:

• Pathogens can spread through: Direct contact Aerosols Body fluids Water Insects Contaminated food
• Body's natural defenses: Skin: Acts as a barrier Mucus: Blocks and traps pathogens Stomach acid: Dissolves pathogens Hair: Provides an additional barrier

Definition: Pathogens are microorganisms that can cause disease.

Highlight: Understanding how pathogens spread and how the body defends against them is crucial for public health and disease prevention.

Types of Microorganisms

This page covers different types of microorganisms, important for homeostasis biology notes PDF:

• Bacteria cell structure: Cell wall Loose DNA Cytoplasm Cell membrane
• Types of microorganisms: Viruses Fungi Bacteria Protists
• Virus structure: Protein coat Genes $DNA or RNA$

Vocabulary: Protists - A diverse group of eukaryotic microorganisms, including algae and protozoa.

Highlight: Understanding the structure and types of microorganisms is crucial for studying infectious diseases and immune responses.

Natural Selection and Mutations

This page explains natural selection and mutations, key concepts in natural selection rules and mutations WJEC:

• Natural selection involves: Natural variation Inheritance Selection Time Adaptation
• Mutation: A change in DNA molecule resulting in a new gene
• Causes of mutations: Natural radioactivity in the air $40.1$ Direct radioactivity $30.1$ Food and drink $10$ Cosmic radiation $5$ Medical procedures $15$

Definition: Natural selection is the process by which organisms better adapted to their environment tend to survive and produce more offspring.

Highlight: Understanding natural selection and mutations is crucial for explaining evolution and biodiversity, key topics in variation and evolution WJEC A Level Biology.