The Heart

Structure

The heart is the muscular organ that pumps blood to and from the lungs and around the body. The heart consists of four chambers and each chamber is very important.

Right atrium

Deoxygenated blood flows into the right atrium from the body.
The vein that pumps deoxygenated blood into the right atrium is called the vena cava.
The right atrium is the first chamber that deoxygenated blood flows through.

Right ventricle

When the walls of the right atrium contracts, deoxygenated blood flows into the right ventricle.
The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
Then the walls of the right ventricle contracts, blood is pumped out of the pulmonary artery to the lungs.
The semi-lunar valves prevent blood from flowing back into the right ventricle from the pulmonary artery.

Left atrium

Oxygenated blood flows into the left atrium from the lungs.
The vein that pumps oxygenated blood into the left atrium is called the pulmonary vein.

Left ventricle

When the walls of the left atrium contracts, oxygenated blood flows into the left ventricle.
The atrioventricular valves prevent blood from flowing back into the atria from the ventricles.
The walls of the left ventricle are considerably thicker than the right ventricle.
- The left ventricle has to transport blood all the way around the body but the right ventricle only has to transport blood to the lungs.

Aorta

When the left ventricle contracts, blood is pumped out of the heart to the rest of the body.
Oxygenated blood leaves the heart through the aorta.
The semi-lunar valves prevent blood from flowing back into the left ventricle from the aorta.

The Cardiac Cycle

The flow of blood from the lungs to the heart and around the body is called the cardiac cycle. The cardiac cycle is the continuous relaxing and contracting of the heart. The steps involved are:

1) Atrial contraction

Blood from the lungs flows into the left atrium and blood from the body flows into the right atrium simultaneously.
The atria contract, increasing the pressure in the atria.
The blood in the atria is forced into the ventricles.
The ventricles are relaxed and fill with blood.

2) Ventricular contraction

The atria relax and the ventricles start to contract.
Contraction of the ventricles causes the pressure inside the ventricles to increase.
The pressure shuts the atrioventricular valves so that blood does not flow back into the atria.
The blood in the ventricles is forced out of the ventricles and out of the heart through the pulmonary artery or the aorta.

3) Relaxation

The blood in the pulmonary artery and the aorta is at high pressure. -The pressure shuts the semi-lunar valves so that blood does not flow back into the ventricles.
Both the ventricles and the atria relax and the atrioventricular valves reopen.
Blood flows into the ventricles and the atria from the pulmonary vein and vena cava.

4) Repeat

The cycle continues.

Interpreting Data

At each stage in the cardiac cycle, the pressure and volume of the atria and ventricles changes considerably. These changes can be presented as a change over time.

Pressure in the atria

When the atria contract, the pressure in the atria increases.
When the atria relax and the ventricles contract, the pressure in the atria decreases.
When both the atria and the ventricles relax, there is a slight increase as the atria fill with blood again.

Pressure in the ventricles

When the atria contract, the pressure in the ventricles is relatively low. There is a slight increase in pressure as the ventricles fill with blood.
When the ventricles contract, the pressure increases dramatically. The pressure increases considerably more than when the atria contract.
When both the atria and the ventricles relax, there is a slight increase as the ventricles fill with blood again.

Volume in the atria

When the atria contract, the volume in the atria decreases.
When the atria relax and the ventricles contract, the volume in the atria increases again.
When both the atria and the ventricles relax, there is a slight decrease when blood flows into the ventricles from the atria.

Volume in the ventricles

When the atria contract, the volume in the ventricles increases slightly as they fill with blood.
When the ventricles contract, the volume decreases dramatically. The volume decreases considerably more than when the atria contract.
When both the atria and the ventricles relax, the volume increases as the ventricles expand again.

1Cell Biology

2Molecular Biology

2.1Water

2.1.1Water & Hydrogen Bonding

2.1.2IB Multiple Choice - Water & Hydrogen Bonding

2.1.3Extended Response - Water

2.2Carbohydrates & Lipids

2.2.1Monosaccharides

2.2.2Disaccharides & Polysaccharides

2.2.3Triglycerides & Phospholipids

2.2.4Cellulose

2.2.5Starch & Glycogen

2.3Proteins

2.3.1Structure & Functions of Proteins

2.4Enzymes

2.4.1Enzymes

2.4.2Factors Affecting Enzyme Activity

2.4.3Enzyme-Controlled Reactions

2.4.4End of Topic Test - Enzymes

2.5Structure of DNA & RNA

2.5.1DNA & RNA

2.6DNA Replication, Transcription & Translation

2.6.1Protein Synthesis

2.6.2Transcription & Translation

2.6.3End of Topic Test - DNA, Genes & Protein Synthesis

2.6.4Exam-Style Question - Protein Synthesis

2.6.5End of Topic Test - Coronavirus Translation

2.6.6IB Multiple Choice - Transcription

2.6.7IB Multiple Choice - Translation

2.7Cell Respiration

2.7.1Overview of Respiration

2.7.2Anaerobic Respiration

2.7.3End of Topic Test - Anaerobic Respiration

2.7.4Respiration Experiments

2.7.5End of Topic Test - Respiration

2.7.6IB Multiple Choice - Respiration

2.8Photosynthesis

2.8.1Overview of Photosynthesis

3Genetics

4Ecology

4.1Species, Communities & Ecosytems

4.1.1Population Dynamics

4.1.2Communities & Measuring Diversity

4.1.3Relationships Between Populations

4.1.4Overview of Ecosystems

4.1.5Nutrient Cycles

4.1.6Fertilisers

4.1.7Eutrophication

4.1.8Chi-Squared Test

4.2Energy Flow

4.2.1Energy

4.2.2Energy Flow

4.2.3Biomass & Food Chains

4.2.4Heterotrophs & Autotrophs

4.3Carbon Cycle

4.3.1Carbon Cycle

4.4Climate Change

4.4.1Carbon Dioxide

4.4.2The Greenhouse Effect

4.4.3Global Warming

4.4.4Maintaining Biodiversity

5Evolution & Biodiversity

5.1Evidence for Evolution

5.1.1Evidence for Evolution - Fossils & DNA

5.1.2Evidence for Evolution - Anatomy & Geography

5.1.3IB Multiple Choice - Evidence for Evolution

5.1.4Extended Response - DNA & Evolution

5.2Natural Selection

5.2.1Introduction

5.2.2Evolutionary Fitness

5.2.3Natural Selection & Variation

5.2.4End of Topic Quiz - Natural Selection

5.2.5IB Multiple Choice - Natural Selection

5.2.6Speciation

5.3Classification of Biodiversity

5.3.1Introduction to Biodiversity

5.3.2Keystone Species

5.3.3Courtship & Ancestry

5.3.4Classification

5.4Cladistics

5.4.1Evolutionary Relationships

5.4.2IB Multiple Choice - Species & Taxonomy

6Human Physiology

6.1Digestion & Absorption

6.1.1Overview of Digestion

6.1.2Digestion in Mammals

6.1.3Absorption

6.1.4End of Topic Test - Substance Exchange & Digestion

6.1.5End of Topic Test - Substance Ex & Digestion

6.2The Blood System

6.2.1The Circulatory System

6.2.2The Heart

6.2.3Blood Vessels

6.2.4Cardiovascular Disease

6.3Defence Against Infectious Disease

6.3.1Immune System

6.3.2The Immune Response

6.3.3Antibodies

6.3.4Primary & Secondary Response

6.3.5Vaccines

6.3.6HIV

6.3.7End of Topic Test - Immune System

6.3.8Exam-Style Question - Immune System

6.3.9End of Topic Test - Immune System

6.4Gas Exchange

6.4.1Lung Structure & Alveoli

6.4.2Ventilation

6.4.3Lung Disease

6.4.4Lung Disease Data

6.5Neurons & Synapses

6.5.1Neuron Structure

6.5.2Transmission of an Impulse

6.5.3Speed of Transmission

6.5.4End of Topic Test - Neurones & Action Potentials

6.5.5Synapses

6.5.6Types of Synapse

6.5.7Medical Application

6.5.8End of Topic Test - Synapses

6.5.9End of Topic Test - Nervous Comm&Coord

6.6Hormones, HomeoStasis & Reproduction

6.6.1Overview of Homeostasis

6.6.2Blood Glucose Concentration

6.6.3Controlling Blood Glucose Concentration

6.6.4End of Topic Test - Blood Glucose

6.6.5Type I & Type II Diabetes

6.6.6Human Reproductive Systems

6.6.7Hormonal Control of the Menstrual Cycle

7AHL: Nucleic Acids

7.1DNA Structure & Replication

7.1.1DNA

7.1.2RNA

7.1.3DNA Replication

7.1.4DNA Replication - Summary

7.1.5IB Multiple Choice - DNA Replication

7.2Transcription & Gene Expression

7.2.1Introduction to Transcription & Protein Synthesis

7.2.2Types of RNA

7.2.3Transcription

7.2.4RNA Processing in Eukaryotes

7.2.5IB Multiple Choice - Transcription

7.3Translation

7.3.1Translation

7.3.2Retroviruses

7.3.3Scientific Practices: Coronavirus

7.3.4IB Multiple Choice - Translation

8AHL: Metabolism, Cell Respiration & Photosynthesis

8.1Metabolism

8.1.1Molecules to Metabolism

8.2Cell Respiration

8.2.1Glycolysis

8.2.2Aerobic Respiration

8.3Photosynthesis

8.3.1Light-Dependent Reaction

8.3.2Light-Independent Reaction

8.3.3End of Topic Test - Photosynthesis Reactions

8.3.4Limiting Factors

8.3.5Photosynthesis Experiments

8.3.6End of Topic Test - Photosynthesis

8.3.7End of Topic Test - Photosynthesis

9AHL: Plant Biology

9.1Transport in the Xylem of Plants

9.1.1Structure

9.1.2Cohesion-Tension Theory

9.1.3Investigating Transpiration Rate

9.2Transport in the Phloem of Plants

9.2.1Structure

9.2.2Translocation

9.3Growth in Plants

9.3.1Plant Tropisms

10AHL: Genetics & Evolution

10.1Meiosis

10.1.1Stages of Meiosis

10.2Inheritance

10.2.1Linked Genes

10.2.2Sex-Linked Genes

10.2.3Non-Nuclear Inheritance

10.2.4Chi-Squared Test

10.2.5End of Topic Quiz - Inheritance

10.2.6IB Multiple Choice - Non-Mendelian Genetics

10.2.7Introduction to Non-Mendelian Inheritance

10.2.8Extended Response - Inheritance

10.2.9Grade 4-5 (Scientific Practices) - Inheritance

10.3Gene Pools & Speciation

10.3.1Populations

10.3.2Mutations, Genetic Drift, & Gene Flow

10.3.3Speciation

10.3.4Rate of Speciation

10.3.5Allopatric & Sympatric Speciation

11AHL: Animal Physiology

11.1Antibody Production & Vaccination

11.1.1Immune System

11.1.2The Immune Response

11.1.3Antibodies

11.1.4Primary & Secondary Response

11.1.5Vaccines

11.2Movement

11.2.1Skeletal Muscle

11.2.2Sliding Filament Theory

11.2.3Contraction

11.3The Kidney & Osmoregulation

11.3.1Kidneys & Osmoregulation

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