Reflexes

Reflex Actions

Reflex actions allow us to respond to dangerous situations rapidly and automatically. Reflex actions do not involve conscious thought. The nervous system responds to stimuli (events or things) via a reflex arc. Some examples of reflexes are:

Blinking

Sneezing

Dropping hot objects

Components of a Reflex Arc

The different parts of a reflex arc are:

Stimulus

A stimulus can be any change in the environment to which the body needs to respond.
The stimulus is detected by a receptor.

Receptor

Receptors are found all over the body.
They detect the change in the environment and initiate (start) a signalling process within the body.
The signal is picked up by a neurone (nerve cell).

Neurones

There are three types of neurone (nerve cell):
- The sensory neurone, which carries the signal in the form of an electrical impulse to the central nervous system (CNS).
- The relay neurone (in the CNS) relays the electrical impulse from the sensory neurone to the appropriate motor neurone.
- The motor neurone is another type of nerve cell that carries the electrical impulse from the CNS to an effector.

Effector

An effector is a muscle or gland that brings about an action in response to the change in the internal or external environment.

Response

The response can be any action that helps the organism to avoid the harmful situation.

Investigating Human Reaction Times

It is possible to investigate the effects of various factors on human reaction times through a practical experiment.

Testing reaction time

If the reaction time is reduced this means it takes less time to react.
- So, a reduction in the reaction time does NOT mean that someone is reacting more slowly, it means they are reacting more quickly.

Factors

Caffeine and exercise are factors that could affect human reaction time
Their effect can be tested by dropping and catching a ruler.

Procedure

The steps in the practical procedure are:

Hold a ruler vertically from one end. The test subject should have their thumb and finger either side of the ruler at the 0cm mark.
Drop the ruler. The subject should try to catch it between their thumb and forefinger as fast as possible.
Note down the distance from the 0cm mark that the ruler travels before the subject catches it.
Use a table to convert this distance into a reaction time.
Repeat the experiment on a subject who has just had a coffee, or who has just done exercise.
Compare reaction times.

Variables

The independent variable is whether or not the subject has had caffeine or exercised.
The dependent variable is the subject’s reaction time.

1Cell Biology

1.1What's in Cells?

1.1.1Types of Cells

1.1.2Properties of Prokaryotes

1.1.3Standard Form

1.1.4Standard Form - Calculations

1.1.5Addition in Standard Form - Calculations

1.1.6Subtraction in Standard Form - Calculations

1.1.7Multiplication in Standard Form - Calculations

1.1.8Division in Standard Form - Calculations

1.1.9Animal Cells

1.1.10Plant Cells

1.1.11Differences Between Animal & Plant Cells

1.1.12Bacterial Cells

1.1.13Types of Cells HyperLearning

1.1.14Cell Specialisation in Animals

1.1.15Sperm Cells

1.1.16Nerve Cells

1.1.17Muscle Cells

1.1.18Cell Specialisation in Plants

1.1.19Microscopy

1.1.20Developments in Microscopy

1.1.21Microscope Practical

1.1.22Microscopy - Calculations

1.1.23Culturing Microorganisms

1.1.24Contamination

1.1.25Avoiding Contamination

1.1.26Calculating Bacteria

1.1.27Calculating Bacteria - Calculations

1.1.28End of Topic Test - What's in Cells?

1.1.29Exam-Style Questions - Cell Structure & Microscopy

1.2Cell Division

1.2.1Chromosomes

1.2.2The Cell Cycle

1.2.3Mitosis

1.2.4Exam-Style Questions - Mitosis & Cell Cycle

1.2.5Stem Cells

1.2.6Use of Stem Cells

1.2.7Disadvantages of Stem Cells

1.3Transport in Cells

1.3.1Diffusion

1.3.2Factors Affecting Diffusion

1.3.3Surface Area : Volume

1.3.4Surface Area : Volume - Calculations

1.3.5Exchange Surfaces

1.3.6Examples of Exchange Surfaces

1.3.7Osmosis

1.3.8Osmosis Practical

1.3.9Active Transport

1.3.10Transport in Cells

1.3.11End of Topic Test - Cell Division & Transport

1.3.12Grade 9 - Cell Transport

2Organisation

2.1Principles of Organisation

2.1.1Cells & Tissues

2.1.2Organs

2.1.3Organ Systems

2.1.4Organisms

2.2Enzymes

2.2.1Enzymes

2.2.2Enzymes HyperFlashcards

2.2.3Rate of Reaction

2.2.4Calculating Rate of Reaction

2.2.5Rate of Reaction - Calculations

2.2.6Digestion

2.2.7Bile

2.2.8Examples of Digestive Enzymes - Amylase

2.2.9Examples of Digestive Enzymes - Protease

2.2.10Examples of Digestive Enzymes - Lipase

2.2.11Testing for Biological Molecules

2.2.12End of Topic Test - Organisation & Enzymes

2.2.13Grade 9 - Enzymes

2.2.14Exam-Style Questions - Enzymes

2.3Circulatory System

2.3.1Types of Blood Vessel

2.3.2Blood Vessels - Arteries

2.3.3Blood Vessels - Capillaries

2.3.4Blood Vessels - Veins

2.3.5The Heart - Structure

2.3.6The Heart - Function

2.3.7Important Blood Vessels

2.3.8Double Circulatory System

2.3.9Gas Exchange

2.3.10Gas exchange - Calculations

2.3.11Alveoli

2.3.12Blood Components

2.3.13Platelets

2.3.14Red Blood Cells

2.3.15White Blood Cells

2.3.16End of Topic Test - Circulatory System

2.4Non-Communicable Diseases

2.4.1Health Issues

2.4.2Disease Interactions

2.4.3Sampling

2.4.4Sampling - Calculations

2.4.5Risk Factors

2.4.6Examples of Risk Factors

2.4.7Risk Factor Graphs

2.4.8Coronary Heart Disease

2.4.9Heart Valve Disease

2.4.10Heart Failure

2.4.11Treating Heart Disease

2.4.12Cancer

2.4.13Cancer Risk Factors

2.4.14End of Topic Test - Non-Communicable Diseases

2.4.15Exam-Style Questions - Coronary Heart Disease

2.5Plant Tissues, Organs & Systems

2.5.1Plant Tissues

2.5.2Leaves

2.5.3Transpiration

2.5.4Rate of Transpiration

2.5.5Measuring Transpiration

2.5.6Translocation

2.5.7Transpiration Tissues

2.5.8Stomata

2.5.9Premium Knowledge - Transpiration

2.5.10End of Topic Test - Plants

2.5.11Exam-Style Questions - Plant Tissues

3Infection & Response

3.1Communicable Disease

3.1.1Spreading Disease

3.1.2Viruses

3.1.3Other Pathogens

3.1.4Human Defence Systems

3.1.5Human Defence Systems 2

3.1.6Grade 9 - Immune System

3.1.7Antibiotics

3.1.8Drug Development

3.1.9Drug Testing

3.1.10Drug Testing / Efficacy - Calculations

3.1.11End of Topic Test - Communicable Diseases

3.1.12Exam-Style Questions - Microorganisms & Disease

3.2Monoclonal Antibodies

3.2.1Producing & Using Monoclonal Antibodies

3.2.2Grade 9 - Monoclonal Antibodies

3.3Plant Diseases

3.3.1Diseases & Defence

3.3.2Identifying Disease

3.3.3End of Topic Test - Antibodies & Plant Disease

4Bioenergetics

4.1Photosynthesis

4.1.1Photosynthesis

4.1.2Photosynthesis 2

4.1.3Photosynthesis - Calculations

4.1.4Photosynthesis Experiments

4.1.5Grade 9 - Photosynthesis Experiment

4.1.6Exam-Style Questions - Rate of Photosynthesis

4.2Respiration

4.2.1Respiration

4.2.2Respiration - Calculations

4.2.3Exercise

4.2.4Respiration HyperLearning

4.2.5End of Topic Test - Photosynthesis and Respiration

4.2.6Exam-Style Questions - Anaerobic Respiration

5Homeostasis & Response

5.1Homeostasis

5.1.1Homeostasis

5.1.2Homeostasis & Negative Feedback

5.1.3Exam-Style Questions - Exercise & Homeostasis

5.2The Human Nervous System

5.2.1The Nervous System

5.2.2The Nervous System HyperFlashcards

5.2.3Synapses

5.2.4Reflexes

5.2.5Exam-Style Questions - Nervous System

5.2.6The Brain

5.2.7Eye Anatomy

5.2.8Eye Function

5.2.9Control of Body Temperature

5.2.10Warming Up & Cooling Down

5.2.11Body Temperature HyperLearning

5.2.12End of Topic Test - Human Nervous System

5.3Hormonal Coordination in Humans

5.3.1Endocrine System

5.3.2Thyroxine & Adrenaline

5.3.3Blood Glucose

5.3.4Diabetes

5.3.5Control of Water Balance

5.3.6Urine

5.3.7Dialysis

5.3.8Transplants

5.3.9Puberty

5.3.10Menstruation

5.3.11Contraception

5.3.12Contraception 2

5.3.13Hormones for Infertility

5.3.14End of Topic Test - Homeostasis & Hormones

5.3.15Grade 9 - Hormonal Coordination

5.3.16Exam-Style Questions - Hormones & Contraception

5.4Plant Hormones

5.4.1Plant Hormones

5.4.2Plant Hormones 2

5.4.3End of Topic Test - Hormones

6Inheritance, Variation & Evolution

6.1Reproduction

6.1.1Reproduction

6.1.2Reproduction 2

6.1.3Genome

6.1.4DNA

6.1.5Protein Synthesis

6.1.6Genetic Inheritance

6.1.7Genetic Crosses

6.1.8Inherited Disorders

6.1.9Inherited Disorders 2

6.1.10Genetic Crosses - Calculations

6.1.11Genome Screening & Sex Determination

6.1.12End of Topic Test - Reproduction

6.1.13Exam-Style Questions - DNA & Genetics

6.2Variation & Evolution

6.2.1Variation & Evolution

6.2.2Selective Breeding

6.2.3Selective Breeding 2

6.2.4Genetic Engineering

6.2.5Uses of Genetic Modification

6.2.6Cloning

6.2.7Cloning 2

6.2.8End of Topic Test - Variation & Evolution

6.2.9Exam-Style Questions - Selective Breeding

6.3Genetics & Evolution

6.3.1Natural Selection

6.3.2Speciation

6.3.3Evidence for Evolution

6.3.4Genetics & Extinction

6.3.5Grade 9 - Evolution

6.4Classification

6.4.1Classification of Living Organisms

6.4.2Classification of Living Organisms 2

6.4.3End of Topic - Genetics & Classification

7Ecology

7.1Adaptations & Interdependence

7.1.1Communities

7.1.2Communities 2

7.2Organisation of Ecosystems

7.2.1Population Dynamics

7.2.2Environmental Change

7.2.3Assessing Ecosystems

7.2.4Assessing Ecosystems - Calculations

7.2.5The Cycling of Materials

7.2.6Decay

7.2.7Decay Practical

7.2.8End of Topic Test - Organisation of Ecosystems

7.2.9Grade 9 - Ecosystems

7.2.10Exam-Style Questions - Decomposition

7.3Biodiversity

7.3.1Human Interactions with Ecosystems

7.3.2Human Interactions with Ecosystems 2

7.3.3Greenhouse Gases

7.3.4Greenhouse Gases 2

7.3.5Hardest Questions - Humans & the Environment

7.3.6End of Topic Test - Adaptations & Biodiversity

7.4Trophic Levels

7.4.1Trophic Levels

7.4.2Trophic Levels 2

7.4.3Transfer efficiency - Calculations

7.4.4Premium Knowledge - Trophic Levels & Food Chains

7.4.5Exam-Style Questions - Food Chains

7.5Food Production

7.5.1Food Production

7.5.2Farming & Fishing

7.5.3Food Production - Calculations

7.5.4End of Topic Test - Food & Trophic Levels

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