What is a mass transport system?

It is a system that carries substances in bulk over long distances within an organism, usually in a fluid moved through vessels, rather than relying on diffusion.

Why can a single-celled organism survive without a mass transport system?

It has a very large surface area to volume ratio and every part of it is close to the surface, so diffusion alone supplies its needs fast enough.

What happens to the surface area to volume ratio of a mammal as its body size increases?

It decreases, because volume rises with the cube of the linear dimensions while surface area rises only with the square.

Explain why a small surface area to volume ratio makes diffusion alone inadequate in a mammal.

There is too little exchange surface for the mass of respiring tissue, and the distances from the surface to the innermost cells are far too great for diffusion to supply oxygen quickly enough.

Why does a high basal metabolic rate increase the need for a mass transport system?

Oxygen and glucose are consumed rapidly and carbon dioxide is produced rapidly, so these substances must be delivered and removed faster than diffusion could manage.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

Topic overview The cell cycle and mitosis Apoptosis in growth and repair Stem cells and cell differentiation

The Developing Individual: Meiosis, Growth and Development

Topic overview Meiosis, haploid gametes and genetic variation The stages of meiosis Antenatal care and diet in pregnancy Alcohol, smoking and monitoring fetal growth Prenatal screening and karyotypes

The Development of Species: Evolution and Classification

Topic overview Classification and the species concept Evidence for classification and DNA barcoding Phylogenetic trees, hominids and the evolution of language Human adaptations, natural selection and evolution Plant adaptations and how they are investigated Measuring biodiversity and genetic diversity

Cells and Microscopy

Topic overview Microscopy and the cell theory Blood smears, staining and microscope drawings Blood cells and their structure Magnification and measuring cells Haemocytometer cell counts and dilutions Flow cytometry in blood analysis Ultrastructure of the animal cell Plant and prokaryotic cells Membrane lipids and the fluid mosaic model Movement of molecules across membranes The roles of membranes and the secretion of proteins

Water and Its Importance in Plants and Animals

Topic overview The properties of water Water as a transport medium and the composition of body fluids Detecting and measuring sugars and proteins Monomers, polymers and the carbohydrates Osmosis and water potential

Proteins and Enzymes

Topic overview Amino acids, peptide bonds and chromatography Globular protein structure: enzymes and haemoglobin Enzyme action and the rate of reaction Blood clotting and first aid Enzymes and inhibitors in medicine Blood donation and stored blood products

Nucleic Acids

Topic overview Nucleotides, ADP and ATP The structure of DNA and its extraction DNA replication and the genetic code RNA, transcription and translation

Patterns of Inheritance

Topic overview Monogenic inheritance and genetic terminology Gene mutations and inherited disease Codominance, multiple alleles and linkage Model organisms, dihybrid crosses and the chi-squared test Chromosome mutations and genetic counselling

Population Genetics and Epigenetics

Topic overview Natural selection, sickle cell and malaria The Hardy-Weinberg principle Genetic drift, the founder effect and speciation Epigenetics and gene expression

Gene Technologies

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The Principles and Importance of Homeostasis

Topic overview Homeostatic principles, normal ranges and feedback The nervous and hormonal control of heart rate The control of body temperature and the role of thyroxine Measuring core body temperature, hypothermia and hyperthermia

The Hormonal Control of Blood Glucose and the Management of Diabetes

Topic overview The pancreas as an endocrine gland The regulation of blood glucose by negative feedback Types of diabetes and diagnostic testing Treating and managing diabetes

Kidney Functions and Malfunctions

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The Cellular Basis of Cancer and Treatment

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Respiratory Diseases and Treatment

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Cellular Respiration

Topic overview Glycolysis and the link reaction The Krebs cycle Oxidative phosphorylation and anaerobic respiration Respiratory substrates and respiratory quotients Measuring the rate of respiration

Metabolism and Exercise

Topic overview The consequences of exercise on the body Aerobic fitness and VO₂ max Training, F.I.T.T. factors and investigating fitness Enhancing athletic performance Haemoglobin and the transport of oxygen Oxygen dissociation curves of different respiratory pigments Oxygen deficit and oxygen debt The structure of skeletal muscle The sliding filament theory of muscle contraction

Pathogenic Microorganisms

Topic overview How pathogens cause communicable disease Tuberculosis HIV, AIDS and the structure of the virus Identifying bacteria: Gram staining and culture Epidemiology: incidence, prevalence and mortality Notifiable diseases and the control of HIV and TB

The Immune System

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Controlling Communicable Diseases

Topic overview Vaccination and vaccination programmes Problems and ethics of vaccine development and use Antibiotics and antibiotic resistance Investigating antibiotics, disinfectants and hygiene

Photosynthesis, Food Production and Management of the Environment

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The Impact of Population Increase

Topic overview Birth rate, death rate and demographic change Human impact on ecosystems and biodiversity The importance and measurement of species biodiversity Global food security and sustainable food production

Planning and Implementing Practical Work

Topic overview Designing an investigation and controlling variables Choosing apparatus and judging whether a method will work Implementing: apparatus, units and recording results

Analysing and Evaluating Practical Results

Topic overview Processing and interpreting experimental results Mathematical skills for analysing biological data Significant figures and reporting values Plotting and interpreting graphs Anomalies, limitations and refining a procedure Precision, accuracy and uncertainty

Practical Skills, Apparatus and Techniques

Topic overview Investigative approaches and working safely Following instructions, recording and presenting data Research, referencing and processing data with software Measuring mass, volume, time, temperature, length and pH Colorimeters and potometers Laboratory glassware and serial dilutions Light microscopy, graticules and biological drawing Qualitative reagents for biological molecules Chromatography and electrophoresis Aseptic technique and dissection Whole-organism responses, fieldwork sampling and data logging

Fertility and Assisted Reproduction

Topic overview The urinogenital systems and gonad histology Gametogenesis and the structure of the gametes Hormonal control of gametogenesis and the menstrual cycle Fertilisation and pregnancy testing The causes and issues of infertility Assisted reproduction techniques

The Effects of Ageing on the Reproductive System

Topic overview Ageing and the female reproductive system Managing the menopause Ageing and the male urinogenital system

Plant Reproduction

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The Nervous System and the Identification and Consequences of Damage

Topic overview Organisation of the nervous system and nervous tissue The structure and function of the human brain The structure of motor, sensory and relay neurones Resting potential and the action potential Synapses and the integration of responses Reflexes, reaction times and their investigation Brain scans and the consequences of nervous system damage Drugs, brain function and dependency

Monitoring Visual Function

Topic overview The structure of the eye The retina and its role as a transducer Assessing visual function by routine eye tests

The Effect of Ageing on the Nervous System

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The Heart and Monitoring Heart Function

Topic overview The need for a mass transport system Structure and dissection of the mammalian heart The cardiac cycle Initiation and coordination of the heartbeat Heart rate, pulse rate and cardiac output Electrocardiograms and emergency cardiac treatment

Transport Systems in Mammals

Topic overview The closed double circulatory system Blood vessels and their microscopic structure Tissue fluid and capillary exchange Measuring and interpreting blood pressure

Gas Exchange in Mammals and Plants

Topic overview Tissues of the mammalian gas exchange system Gas exchange in the alveoli Pulmonary ventilation and lung volumes Expired air resuscitation Gas exchange and stomata in terrestrial plants

Transport Systems in Plants

Topic overview The need for transport systems in plants Vascular tissue in roots, stems and leaves Water uptake and movement through the plant Transpiration and Its Measurement Translocation in the Phloem

The Heart and Monitoring Heart Function

The need for a mass transport system

3 things to know
Components 01, 02 and 03

Overview

Recall questions on mass transport systems, why single-celled organisms manage by diffusion, surface area to volume ratio and its calculation, how size, multicellularity and metabolic rate create a need for mass transport, and what the mammalian blood system carries.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

State the relationship used to compare the exchange capacity of organisms of different sizes.

Key term

Explain how being multicellular creates a need for mass transport.

Numbers

A cube-shaped block of tissue has sides of 2 cm. Calculate its surface area to volume ratio.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a mass transport system?
Model answer
It is a system that carries substances in bulk over long distances within an organism, usually in a fluid moved through vessels, rather than relying on diffusion.
2
Why can a single-celled organism survive without a mass transport system?
Model answer
It has a very large surface area to volume ratio and every part of it is close to the surface, so diffusion alone supplies its needs fast enough.
3
State the relationship used to compare the exchange capacity of organisms of different sizes.
Model answer
Ratio = surface area ÷ volume.
4
What happens to the surface area to volume ratio of a mammal as its body size increases?
Model answer
It decreases, because volume rises with the cube of the linear dimensions while surface area rises only with the square.
5
Explain why a small surface area to volume ratio makes diffusion alone inadequate in a mammal.
Model answer
There is too little exchange surface for the mass of respiring tissue, and the distances from the surface to the innermost cells are far too great for diffusion to supply oxygen quickly enough.
6
Why does a high basal metabolic rate increase the need for a mass transport system?
Model answer
Oxygen and glucose are consumed rapidly and carbon dioxide is produced rapidly, so these substances must be delivered and removed faster than diffusion could manage.

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The Developing Cell: Cell Division and Cell Differentiation

The Developing Individual: Meiosis, Growth and Development

The Development of Species: Evolution and Classification

Cells and Microscopy

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