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Ordinary Level Revision Notes
Leaving Cert Ordinary Level Biology
Chapter 15: Human Anatomy and Physiology
Body Systems & Homeostasis
Subtopics Covered
- Learning Outcomes
- Body Systems Overview
- Circulatory System: Blood
- Blood Vessels
- Heart and Double Circulation
- Pulse Control and Lymphatic System
What This Pack Includes
- Structured chapter notes formatted for ExamsLogic website reading
- Exam-focused diagrams, definitions, and worked examples
- Interactive practice sections carried over from the source notes
- Independent study guidance based on the official curriculum
- Print-friendly layout for future PDF export when needed
This publication is an independent educational resource developed by ExamsLogic and compiled by experienced educators. It is based on publicly available official curricula, including Cambridge, Pearson Edexcel, IB, and the Irish Leaving Certificate. This product is not endorsed by, affiliated with, or sponsored by any examination board or governing authority. All registered trademarks remain the property of their respective owners.
1. Learning Outcomes
- Describe the structure and function of major human body systems.
- Explain the composition and functions of blood.
- Compare arteries, veins and capillaries.
- Trace blood through the heart and double circulation.
- Describe digestion, breathing, excretion, nervous control and endocrine control.
- Explain skeleton, joints, muscles and immune defences.
- Describe human reproduction and the main stages from fertilisation to birth.
- Identify the major structures and functions of the eye and ear.
HL-only awareness: Detailed nephron processes, detailed T-cell/B-cell functions and advanced hormonal control are Higher Level. This OL chapter keeps the required concepts clear and exam-ready.
2. Body Systems Overview
Transport
Circulatory, lymphatic and digestive systems move materials around the body.
Control
Nervous and endocrine systems coordinate fast and slow responses.
Protection
Immune, skeletal and skin barriers help defend and support the body.
Biology link: Systems do not work alone. For example, digestion supplies glucose, breathing supplies oxygen, and blood transports both for respiration.
3. Circulatory System: Blood
| Blood component | Main function | Exam detail |
|---|---|---|
| Plasma | Liquid part transporting dissolved substances. | Carries nutrients, hormones, carbon dioxide, urea and heat. |
| Red blood cells | Transport oxygen. | Contain haemoglobin and lack a nucleus at maturity. |
| White blood cells | Defend against disease. | Some engulf pathogens; some make antibodies. |
| Platelets | Help blood clot. | Prevent excessive bleeding and entry of microbes. |
Exam Tip: Red blood cells carry oxygen; white blood cells defend; platelets clot; plasma transports dissolved substances.
4. Blood Vessels
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Direction | Away from heart. | Towards heart. | Between arteries and veins. |
| Wall | Thick, muscular and elastic. | Thinner wall. | One cell thick. |
| Lumen | Narrow. | Wide. | Very narrow. |
| Valves | No valves usually. | Valves present. | No valves. |
| Pressure | High. | Low. | Low and slow for exchange. |
Examiner Trap: Arteries do not always carry oxygenated blood. The pulmonary artery carries deoxygenated blood to the lungs.
5. Heart and Double Circulation
The heart is a muscular pump with four chambers: right atrium, right ventricle, left atrium and left ventricle. Valves prevent backflow.
Body→Right heart→Lungs→Left heart→Body
Examiner Secret: Double circulation means blood passes through the heart twice in one complete circuit: once to lungs and once to body.
6. Pulse Control and Lymphatic System
| Topic | Key idea |
|---|---|
| Pulse | The pulse is caused by pressure waves in arteries when the heart contracts. |
| Heart rate control | Heart rate increases during exercise to deliver more oxygen and glucose and remove carbon dioxide faster. |
| Lymph | Tissue fluid that enters lymph vessels and is returned to the blood. |
| Lymph nodes | Filter lymph and contain white blood cells that help fight infection. |
Common Mistake: Saying pulse is blood moving in veins. Pulse is normally felt in arteries.
7. Digestive System Overview
| Part | Main function |
|---|---|
| Mouth | Mechanical digestion by teeth; chemical digestion of starch begins with amylase. |
| Oesophagus | Moves food to stomach by peristalsis. |
| Stomach | Churns food; acid kills bacteria; protease digests protein. |
| Liver | Produces bile and processes absorbed nutrients. |
| Gall bladder | Stores bile. |
| Pancreas | Produces digestive enzymes and hormones such as insulin. |
| Small intestine | Digestion completed and nutrients absorbed by villi. |
| Large intestine | Water reabsorbed; faeces formed. |
Mouth→Oesophagus→Stomach→Small intestine→Large intestine→Anus
8. Mechanical vs Chemical Digestion and Villi
| Type | Meaning | Example |
|---|---|---|
| Mechanical digestion | Physical breakdown of food into smaller pieces. | Chewing; stomach churning. |
| Chemical digestion | Enzymes break large food molecules into smaller soluble molecules. | Amylase breaks starch; protease breaks protein; lipase breaks fat. |
| Peristalsis | Muscular waves moving food through the alimentary canal. | Oesophagus and intestines. |
Exam Tip: Villi are adapted for absorption by large surface area, thin walls and rich blood supply.
9. Dental Formula and Portal Circulation
| Topic | OL explanation |
|---|---|
| Dental formula | A shorthand way to show number and type of teeth in half of upper and lower jaws. |
| Human adult teeth | Incisors cut, canines tear, premolars and molars grind. |
| Portal circulation | Blood from the small intestine travels to the liver through the hepatic portal vein before returning to general circulation. |
| Why portal circulation matters | The liver processes, stores and detoxifies absorbed substances. |
Examiner Secret: Nutrients absorbed by the small intestine do not go straight everywhere first; they go to the liver via the hepatic portal vein.
10. Breathing System
| Structure | Function |
|---|---|
| Nose/nasal cavity | Warms, moistens and filters air. |
| Trachea | Air passage supported by cartilage rings. |
| Bronchi | Two main branches into lungs. |
| Bronchioles | Smaller airways. |
| Alveoli | Gas exchange surfaces. |
| Diaphragm | Muscle helping ventilation. |
| Intercostal muscles | Move ribs during breathing. |
Inhalation
Diaphragm contracts and flattens. External intercostal muscles lift ribs up and out. Thorax volume increases, pressure decreases, air enters.
Exhalation
Diaphragm relaxes and domes upward. Ribs move down and in. Thorax volume decreases, pressure increases, air leaves.
11. Gas Exchange and Breathing Rate Control
| Alveolus adaptation | How it helps gas exchange |
|---|---|
| Large surface area | More space for diffusion. |
| Thin walls | Short diffusion distance. |
| Moist surface | Gases dissolve before diffusion. |
| Rich blood supply | Maintains steep concentration gradients. |
Oxygen diffuses: alveoli → blood
Carbon dioxide diffuses: blood → alveoli
Carbon dioxide diffuses: blood → alveoli
Examiner Trap: Low oxygen matters, but carbon dioxide level is a major control factor for breathing rate.
12. Excretory System
| Excretory organ | Waste removed |
|---|---|
| Lungs | Carbon dioxide and water vapour. |
| Skin | Water, salts and small amounts of urea in sweat. |
| Kidneys | Urea, excess water and salts in urine. |
| Kidney structure | Function |
|---|---|
| Cortex | Outer region containing many nephron parts. |
| Medulla | Inner region involved in urine concentration. |
| Pelvis | Collects urine before it enters ureter. |
| Ureter | Carries urine to bladder. |
| Bladder | Stores urine. |
| Urethra | Carries urine out of body. |
HL-only awareness: Detailed ultrafiltration, selective reabsorption and ADH water-balance control are Higher Level. OL students should know kidneys filter blood and remove urea/excess water/salts.
13. Nervous System
| Part | Meaning |
|---|---|
| CNS | Central nervous system: brain and spinal cord. |
| PNS | Peripheral nervous system: nerves outside CNS. |
| Sensory neuron | Carries impulses from receptors to CNS. |
| Interneuron/relay neuron | Connects neurons in CNS. |
| Motor neuron | Carries impulses from CNS to effectors. |
| Synapse | Junction between neurons where chemicals transmit signals. |
Stimulus→Receptor→Sensory neuron→CNS→Motor neuron→Effector→Response
Exam Tip: Reflex actions are fast, automatic and protective.
14. Endocrine System
| Gland/type | Key idea |
|---|---|
| Exocrine gland | Releases substances through ducts, e.g. salivary glands. |
| Endocrine gland | Releases hormones directly into blood. |
| Pituitary | Master gland; controls other glands and growth. |
| Thyroid | Controls metabolic rate using thyroxine. |
| Pancreas | Controls blood glucose using insulin and glucagon. |
| Adrenal glands | Release adrenaline for fight-or-flight responses. |
Negative feedback: A control mechanism that reverses a change and returns the body toward normal conditions.
Examiner Trap: Hormones travel in blood and act more slowly than nerve impulses, but their effects may last longer.
15. Musculoskeletal System
| Structure | Function |
|---|---|
| Axial skeleton | Skull, vertebral column, ribs and sternum; support and protection. |
| Appendicular skeleton | Limbs and girdles; movement. |
| Compact bone | Strong outer bone. |
| Spongy bone | Light inner bone with spaces. |
| Medullary cavity | Contains bone marrow. |
| Cartilage | Smooth tissue reducing friction and cushioning joints. |
| Ligament | Connects bone to bone. |
| Tendon | Connects muscle to bone. |
Antagonistic muscles
Muscles work in pairs. When one contracts, the other relaxes.
Example
Biceps contracts and triceps relaxes to bend the arm; triceps contracts and biceps relaxes to straighten it.
16. Immune System
| Defence | Type | Function |
|---|---|---|
| Skin | General defence | Physical barrier preventing pathogen entry. |
| Mucous membranes | General defence | Trap pathogens in mucus. |
| Phagocytic WBCs | General defence | Engulf and digest pathogens. |
| Antigens | Specific defence trigger | Foreign markers recognised by immune system. |
| Antibodies | Specific defence proteins | Bind to specific antigens. |
| Active immunity | Body makes its own antibodies. | Longer lasting, e.g. vaccination or infection. |
| Passive immunity | Antibodies received from another source. | Shorter lasting, e.g. mother to baby. |
HL-only awareness: Detailed T-cell and B-cell functions are Higher Level. OL students should understand antigens, antibodies and active vs passive immunity.
17. Human Reproduction
Male system
- Testes produce sperm and testosterone.
- Sperm ducts carry sperm.
- Prostate/seminal glands add fluid to semen.
- Penis transfers semen during copulation.
Female system
- Ovaries produce ova and hormones.
- Fallopian tubes carry ova and are usual site of fertilisation.
- Uterus supports embryo/foetus development.
- Cervix and vagina are involved in birth and copulation.
| Hormone | Main role in menstrual cycle |
|---|---|
| FSH | Stimulates follicle development in ovary. |
| Oestrogen | Repairs/thickens uterus lining and helps trigger LH surge. |
| LH | Triggers ovulation. |
| Progesterone | Maintains uterus lining after ovulation. |
Copulation→Fertilisation→Implantation→Embryo development→Birth→Lactation
18. Sensing Organs: Eye and Ear
| Eye part | Function |
|---|---|
| Cornea | Refracts light into eye. |
| Iris | Controls pupil size. |
| Pupil | Opening allowing light in. |
| Lens | Focuses light on retina. |
| Retina | Contains light receptors. |
| Optic nerve | Carries impulses to brain. |
| Ear part | Function |
|---|---|
| Pinna | Collects sound waves. |
| Eardrum | Vibrates when sound waves arrive. |
| Ossicles | Amplify vibrations. |
| Cochlea | Converts vibrations into nerve impulses. |
| Auditory nerve | Carries impulses to brain. |
| Semicircular canals | Help balance. |
19. Interactive Simulator: Human System Detective
Identify the System
Clue: Transports oxygen, nutrients, hormones and wastes.
Feedback
Ready
Match the function to the correct system.
20. Interactive Simulator: Structure Function Match
Choose the Function
Structure: Platelets
Feedback
Ready
Think of the structure's main exam function.
21. High-Value Exam Guidance
Exam Tip 1: Always compare vessels using wall thickness, lumen, valves, pressure and direction.
Exam Tip 2: For villi and alveoli, use the same logic: large surface area, thin walls and good blood supply.
Exam Tip 3: Reflex arcs must be written in correct order.
Exam Tip 4: Active immunity = body makes antibodies; passive immunity = antibodies received.
Examiner Trap 1: Urea is excreted by kidneys, not egested from the digestive system.
Examiner Trap 2: Tendons and ligaments are not the same. Tendon = muscle to bone; ligament = bone to bone.
Common Mistake 1: Saying veins always carry deoxygenated blood. Pulmonary vein carries oxygenated blood.
Common Mistake 2: Confusing FSH and LH. LH triggers ovulation.
Examiner Secret 1: The body keeps stable internal conditions using feedback and coordinated systems.
Examiner Secret 2: Many marks come from correct sequence: blood pathway, alimentary canal, reflex arc and reproduction stages.
22. MCQs with Instant Answers
1. Which blood component transports oxygen?
Answer: A. Red blood cells contain haemoglobin and transport oxygen.
2. Which vessel has valves?
Answer: A. Veins contain valves to prevent backflow.
3. Villi are found in the:
Answer: A. Villi absorb digested nutrients in the small intestine.
4. Gas exchange occurs in the:
Answer: A. Alveoli are the gas exchange surfaces of the lungs.
5. The kidney removes mainly:
Answer: A. Kidneys excrete urea, excess water and salts.
6. The CNS consists of:
Answer: A. CNS means central nervous system: brain and spinal cord.
7. Insulin is produced by the:
Answer: A. The pancreas produces insulin.
8. A tendon connects:
Answer: A. Tendons connect muscles to bones.
9. Antibodies bind to:
Answer: A. Antibodies bind specifically to antigens.
10. LH triggers:
Answer: A. LH triggers ovulation.
23. Structured Exam Questions
- Describe the composition and functions of blood. [8]
- Compare arteries, veins and capillaries. [9]
- Trace the double-circulation pathway through the heart, lungs and body. [8]
- Describe the main organs of the digestive system and their functions. [10]
- Compare mechanical and chemical digestion and explain peristalsis. [6]
- Explain how villi are adapted for absorption. [6]
- Describe inhalation and exhalation. [8]
- Explain gas exchange at the alveoli. [6]
- Name three excretory organs and the wastes they remove. [6]
- Describe a reflex arc. [7]
- Compare nervous and endocrine control. [6]
- Explain active and passive immunity. [6]
- Describe the roles of FSH, oestrogen, LH and progesterone. [8]
- State the functions of main eye and ear structures. [8]
24. Detailed Mark Scheme
Q1. Plasma transports dissolved substances [2]. RBCs carry oxygen/haemoglobin [2]. WBCs defend against disease/phagocytosis/antibodies [2]. Platelets clot blood [2].
Q2. Arteries away from heart/thick wall/narrow lumen/high pressure/no valves [3]. Veins to heart/thinner wall/wide lumen/low pressure/valves [3]. Capillaries one-cell thick/exchange/narrow/low pressure [3].
Q3. Body to right atrium/right ventricle [2], pulmonary artery to lungs [1], oxygenated blood returns by pulmonary vein to left atrium [2], left ventricle pumps via aorta to body [2], valves prevent backflow [1].
Q4. Award marks for mouth, oesophagus, stomach, liver, pancreas, small intestine, large intestine, rectum/anus with correct functions. Max 10.
Q5. Mechanical digestion physical breakdown [2]. Chemical digestion enzyme breakdown [2]. Peristalsis muscular waves moving food [2].
Q6. Large surface area [2], thin wall [1], good blood supply [1], lacteal absorbs fats [1], many villi/microvilli [1].
Q7. Inhalation: diaphragm contracts/flattens [1], ribs up/out [1], volume increases [1], pressure decreases/air enters [1]. Exhalation: diaphragm relaxes/domes [1], ribs down/in [1], volume decreases [1], pressure increases/air leaves [1].
Q8. Oxygen diffuses from alveoli to blood [2]. Carbon dioxide diffuses from blood to alveoli [2]. Thin walls/large surface area/good blood supply maintain diffusion [2].
Q9. Lungs remove CO2/water vapour [2]. Skin removes water/salts/small urea [2]. Kidneys remove urea/excess water/salts [2].
Q10. Stimulus [1], receptor [1], sensory neuron [1], CNS/relay neuron [1], motor neuron [1], effector [1], response [1].
Q11. Nervous fast/electrical impulses/nerves/short-lived [3]. Endocrine slower/hormones in blood/longer-lasting [3].
Q12. Active immunity: body makes own antibodies [2], long-lasting [1]. Passive immunity: antibodies received from another source [2], short-lived [1].
Q13. FSH follicle development [2], oestrogen repairs/thickens uterus lining [2], LH triggers ovulation [2], progesterone maintains uterus lining [2].
Q14. Award correct structure-function matches for eye and ear parts. Max 8.
Q2. Arteries away from heart/thick wall/narrow lumen/high pressure/no valves [3]. Veins to heart/thinner wall/wide lumen/low pressure/valves [3]. Capillaries one-cell thick/exchange/narrow/low pressure [3].
Q3. Body to right atrium/right ventricle [2], pulmonary artery to lungs [1], oxygenated blood returns by pulmonary vein to left atrium [2], left ventricle pumps via aorta to body [2], valves prevent backflow [1].
Q4. Award marks for mouth, oesophagus, stomach, liver, pancreas, small intestine, large intestine, rectum/anus with correct functions. Max 10.
Q5. Mechanical digestion physical breakdown [2]. Chemical digestion enzyme breakdown [2]. Peristalsis muscular waves moving food [2].
Q6. Large surface area [2], thin wall [1], good blood supply [1], lacteal absorbs fats [1], many villi/microvilli [1].
Q7. Inhalation: diaphragm contracts/flattens [1], ribs up/out [1], volume increases [1], pressure decreases/air enters [1]. Exhalation: diaphragm relaxes/domes [1], ribs down/in [1], volume decreases [1], pressure increases/air leaves [1].
Q8. Oxygen diffuses from alveoli to blood [2]. Carbon dioxide diffuses from blood to alveoli [2]. Thin walls/large surface area/good blood supply maintain diffusion [2].
Q9. Lungs remove CO2/water vapour [2]. Skin removes water/salts/small urea [2]. Kidneys remove urea/excess water/salts [2].
Q10. Stimulus [1], receptor [1], sensory neuron [1], CNS/relay neuron [1], motor neuron [1], effector [1], response [1].
Q11. Nervous fast/electrical impulses/nerves/short-lived [3]. Endocrine slower/hormones in blood/longer-lasting [3].
Q12. Active immunity: body makes own antibodies [2], long-lasting [1]. Passive immunity: antibodies received from another source [2], short-lived [1].
Q13. FSH follicle development [2], oestrogen repairs/thickens uterus lining [2], LH triggers ovulation [2], progesterone maintains uterus lining [2].
Q14. Award correct structure-function matches for eye and ear parts. Max 8.
25. Mastery Checklist
- I can describe blood components and functions.
- I can compare arteries, veins and capillaries.
- I can trace double circulation.
- I can describe digestion and absorption.
- I can explain ventilation and gas exchange.
- I can identify excretory organs and kidney function.
- I can describe neurons, synapses and reflex arcs.
- I can compare nervous and endocrine control.
- I can explain negative feedback simply.
- I can describe skeleton, joints, tendons, ligaments and antagonistic muscles.
- I can compare general and specific immunity.
- I can describe male and female reproductive systems.
- I can explain menstrual hormones at OL level.
- I can identify eye and ear structures and functions.