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OCR Gateway GCSE Biology

Revision Notes

Home / GCSE / Biology / OCR Gateway / Revision Notes / 2. Scaling Up / 2.2 The Challenges of Size / 2.2.5 Blood Composition


2.2.5 Blood Composition


Red Blood Cells

Blood as a transport system

  • The role of blood in the body is to act as a transport system carrying useful substances to every cell of the body, and carrying harmful waste substances to other organs for processing and/or excretion
    • It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet)
      • Blood consists predominantly of red blood cells and plasma
        • Over half of the volume of the blood is made up of plasma
        • The majority of the other half is made up of red blood cells
      • Less than 1% of blood contains white blood cells and platelets

Blood micrograph, IGCSE & GCSE Biology revision notes

Blood micrograph

The components of the blood 1, downloadable IGCSE & GCSE Biology revision notes

Composition of human blood

Red blood cells carry oxygen

  • Red blood cells are specialised cells that carry oxygen from the lungs to cells throughout the body
  • The structure of red blood cells are adapted for this function in 3 key ways
    • Red blood cells are small with a 'biconcave disk' shape which gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out
    • They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
    • They have no nucleus which allows more space for haemoglobin to be packed in
    • Their small size and flexibility allows them to pass through capillaries

Red Blood Cells, IGCSE & GCSE Biology revision notes

Red blood cells

Blood Plasma

  • Plasma is a straw coloured liquid which the other components of the blood are suspended within
  • Plasma is important for the transport of many substances including:
    • Red blood cells, white blood cells and platelets
    • Water
    • Carbon dioxide - the waste product of cellular respiration
    • Digested food and mineral ions - absorbed from the small intestine and delivered to cells around the body
    • Urea - the waste substance produced in the breakdown of proteins by the liver. Urea is dissolved in the plasma and transported to the kidneys
    • Hormones - chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of the body
    • Antibodies - which are special proteins to help fight infection
    • Heat energy - created in respiration (an exothermic reaction), heat energy is transferred to cooler parts of the body or to the skin where heat can be lost



  • 1. Cell Level Systems
    • 1.1 Cell Structures
      • 1.1.1 Light Microscopes
        • 1.1.2 Cell Structure
          • 1.1.3 Electron Microscopes
          • 1.2 What Happens in Cells (& What do Cells Need?)
            • 1.2.1 DNA Structure
              • 1.2.2 Nucleotides
                • 1.2.3 Protein Synthesis
                  • 1.2.4 The Mechanism of Enzyme Action
                  • 1.3 Respiration
                    • 1.3.1 Respiration is a Chemical Process
                      • 1.3.2 Aerobic & Anaerobic Respiration
                        • 1.3.3 Biological Molecules
                          • 1.3.4 Tests for Biological Molecules
                          • 1.4 Photosynthesis
                            • 1.4.1 Photosynthetic Organisms as Producers
                              • 1.4.2 The Effect of 3 Factors on Photosynthesis
                                • 1.4.3 Limiting Factors - Photosynthesis
                              • 2. Scaling Up
                                • 2.1 Supplying the Cell
                                  • 2.1.1 Cellular Transport - Diffusion & Osmosis
                                    • 2.1.2 Cellular Transport - Active Transport
                                      • 2.1.3 Mitosis & the Cell Cycle
                                        • 2.1.4 Cell Differentiation
                                          • 2.1.5 Stem Cells in Animals & Plants
                                            • 2.1.6 Embryonic & Adult Stem Cells in Animals
                                            • 2.2 The Challenges of Size
                                              • 2.2.1 Surface Area: Volume Ratio & Transport
                                                • 2.2.2 Transport Into & Out of Organisms
                                                  • 2.2.3 The Heart
                                                    • 2.2.4 Blood Vessels
                                                      • 2.2.5 Blood Composition
                                                        • 2.2.6 Transport of Water & Mineral Ions in Plants
                                                          • 2.2.7 Transpiration & Translocation
                                                            • 2.2.8 Xylem & Phloem
                                                              • 2.2.9 Affecting Water Uptake by a Plant
                                                            • 3. Organism Level Systems
                                                              • 3.1 Coordination & Control – the Nervous System
                                                                • 3.1.1 The Nervous System - Structure
                                                                  • 3.1.2 Generating a Nervous Response
                                                                    • 3.1.3 The Reflex Arc
                                                                      • 3.1.4 The Eye
                                                                        • 3.1.5 The Brain
                                                                          • 3.1.6 Investigating Brain Function
                                                                          • 3.2 Coordination & Control – the Endocrine System
                                                                            • 3.2.1 Hormonal Control
                                                                              • 3.2.2 Thyroxine & Adrenaline
                                                                                • 3.2.3 Hormones in Human Reproduction
                                                                                  • 3.2.4 Four Hormones in the Menstrual Cycle
                                                                                    • 3.2.5 Contraception
                                                                                      • 3.2.6 Hormones to Treat Infertility
                                                                                        • 3.2.7 Plant Hormones - Tropisms
                                                                                          • 3.2.8 Use of Plant Hormones by Humans
                                                                                          • 3.3 Maintaining Internal Environments
                                                                                            • 3.3.1 Constant Internal Environment
                                                                                              • 3.3.2 The Skin in Temperature Control
                                                                                                • 3.3.3 Insulin in Blood Sugar Control
                                                                                                  • 3.3.4 Glucagon in Blood Sugar Control
                                                                                                    • 3.3.5 Osmotic Changes in Body Fluids
                                                                                                      • 3.3.6 The Kidneys
                                                                                                        • 3.3.7 ADH in Water Reabsorption
                                                                                                          • 3.3.8 Responses to Extremes
                                                                                                        • 4. Community Level Systems
                                                                                                          • 4.1 Ecosystems
                                                                                                            • 4.1.1 The Cycling of Materials
                                                                                                              • 4.1.2 The Carbon Cycle
                                                                                                                • 4.1.3 Decomposition & Decay
                                                                                                                  • 4.1.4 Levels of Organisation in an Ecosystem
                                                                                                                    • 4.1.5 Abiotic & Biotic Factors
                                                                                                                      • 4.1.6 Interdependence & Competition
                                                                                                                        • 4.1.7 Trophic Levels of Organisms
                                                                                                                          • 4.1.8 Pyramids of Biomass & Biomass Transfers
                                                                                                                        • 5. Genes, Inheritance & Selection
                                                                                                                          • 5.1 Inheritance
                                                                                                                            • 5.1.1 The Genome & Genetics
                                                                                                                              • 5.1.2 Variation
                                                                                                                                • 5.1.3 Influence of Genetic Variants on Phenotype
                                                                                                                                  • 5.1.4 Sexual Reproduction
                                                                                                                                    • 5.1.5 Asexual Reproduction
                                                                                                                                      • 5.1.6 Inheritance
                                                                                                                                        • 5.1.7 The History of Genetics
                                                                                                                                        • 5.2 Natural Selection & Evolution
                                                                                                                                          • 5.2.1 Genetic Variation Within a Population
                                                                                                                                            • 5.2.2 Evolution Through Natural Selection
                                                                                                                                              • 5.2.3 Classification
                                                                                                                                            • 6. Global Challenges
                                                                                                                                              • 6.1 Monitoring & Maintaining the Environment
                                                                                                                                                • 6.1.1 The Distribution & Abundance of Organisms
                                                                                                                                                  • 6.1.2 Human Interactions Within Ecosystems
                                                                                                                                                    • 6.1.3 Maintaining Biodiversity
                                                                                                                                                      • 6.1.4 The Impact of Environmental Changes
                                                                                                                                                      • 6.2 Feeding the Human Race
                                                                                                                                                        • 6.2.1 Food Security
                                                                                                                                                          • 6.2.2 Selective Breeding of Food Products
                                                                                                                                                            • 6.2.3 Genetic Engineering
                                                                                                                                                              • 6.2.4 The Process of Genetic Engineering
                                                                                                                                                                • 6.2.5 Biotechnology & Human Population
                                                                                                                                                                • 6.3 Monitoring & Maintaining Health
                                                                                                                                                                  • 6.3.1 Health & Disease: Disease Types
                                                                                                                                                                    • 6.3.2 Communicable Diseases
                                                                                                                                                                      • 6.3.3 Plant Disease - Detection & Identification
                                                                                                                                                                        • 6.3.4 White Blood Cells & Platelets
                                                                                                                                                                          • 6.3.5 Non-Specific Defences
                                                                                                                                                                            • 6.3.6 The Human Immune System
                                                                                                                                                                              • 6.3.7 Monoclonal Antibodies
                                                                                                                                                                                • 6.3.8 Vaccines Against Disease
                                                                                                                                                                                  • 6.3.9 Developing New Medicines
                                                                                                                                                                                    • 6.3.10 Non-Communicable Human Diseases
                                                                                                                                                                                      • 6.3.11 Stem Cells in Medicine
                                                                                                                                                                                        • 6.3.12 Gene Technology in Medicine
                                                                                                                                                                                      • 7. Practical Skills
                                                                                                                                                                                        • 7.1 Practical Skills
                                                                                                                                                                                          • 7.1.1 Practical - Using Light Microscopes to View Cells
                                                                                                                                                                                            • 7.1.2 Practical - Testing for Food Molecules
                                                                                                                                                                                              • 7.1.3 Practical - DNA Extraction
                                                                                                                                                                                                • 7.1.4 Practical - Sampling Techniques - Quadrats
                                                                                                                                                                                                  • 7.1.5 Practical - Investigating Enzymatic Reactions
                                                                                                                                                                                                    • 7.1.6 Practical - Investigating Photosynthesis
                                                                                                                                                                                                      • 7.1.7 Practical - Investigating Respiration
                                                                                                                                                                                                        • 7.1.8 Practical - Using a Potometer
                                                                                                                                                                                                          • 7.1.9 Practical - Measurement of Stomatal Density
                                                                                                                                                                                                            • 7.1.10 Practical - Aseptic Technique
                                                                                                                                                                                                              • 7.1.11 Practical - Surface Area: Volume Ratio
                                                                                                                                                                                                                • 7.1.12 Practical - Investigating Osmosis


                                                                                                                                                                                                                DOWNLOAD PDF

                                                                                                                                                                                                              Author: Adam



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