Explain how the broad, flat shape of a leaf suits it for photosynthesis.

It gives a large surface area, so the leaf can absorb as much light and carbon dioxide as possible.

Explain why a leaf with a large surface area to volume ratio exchanges gases efficiently.

There is a lot of surface for each unit of volume, so carbon dioxide and oxygen can diffuse in and out fast enough to supply all the cells.

Explain the function of the air spaces in the spongy mesophyll of a leaf.

They allow carbon dioxide to diffuse quickly to the photosynthesising cells and oxygen and water vapour to diffuse away.

Describe the function of the waxy cuticle on a leaf.

It is a waterproof layer that reduces the amount of water evaporating from the leaf surface.

Edexcel GCSE Biology 1BI0

Key Concepts in Biology

Topic overview Eukaryotic and prokaryotic cells Specialised cells and their adaptations Microscopes and magnification calculations Size, scale and units in cell biology Enzyme action and denaturation Factors affecting enzyme activity Enzymes in synthesis and digestion, and rate calculations Food tests and the energy in food Diffusion, osmosis and active transport Osmosis in potatoes and percentage change in mass

Cells and Control

Topic overview Mitosis and the cell cycle Why mitosis matters: growth, repair and cancer Growth, differentiation and percentile charts Stem cells and their use in medicine The structure and function of the brain Investigating and treating the brain Neurones, receptors and the reflex arc The structure and function of the eye Eye defects and how they are corrected

Genetics

Topic overview Asexual and sexual reproduction Meiosis and the formation of gametes DNA structure, genes and the genome Extracting DNA from fruit Protein synthesis: transcription and translation Genetic variants in coding and non-coding DNA Mendel's work and the inheritance of blood groups Alleles, genotype and phenotype Monohybrid crosses and sex determination Probability and ratios from genetic crosses Sex-linked disorders Causes of variation: genes and environment The Human Genome Project Genetic variation and the effects of mutation

Natural Selection and Genetic Modification

Topic overview Darwin, Wallace and the theory of evolution Natural selection and antibiotic resistance Fossil evidence for human evolution Stone tool evidence for human evolution The pentadactyl limb and the three domains Selective breeding Tissue culture Genetic engineering and modern agriculture The stages of genetic engineering Benefits and risks of GM organisms

Health, Disease and the Development of Medicines

Topic overview Health, disease and susceptibility Pathogens and common infections How pathogens spread, and the virus life cycle Sexually transmitted infections How plants defend themselves and how plant disease is detected Physical barriers and chemical defences The immune system, immunisation and herd immunity Antibiotics and developing new medicines Aseptic technique in culturing microorganisms Testing antiseptics and antibiotics on bacterial cultures Monoclonal antibodies Lifestyle factors and non-communicable disease Treatments for cardiovascular disease

Plant Structures and Their Functions

Topic overview Photosynthesis as an endothermic reaction Limiting factors in photosynthesis Light intensity and the rate of photosynthesis Root hair cells, xylem and phloem Transpiration and translocation Leaf structure for photosynthesis and gas exchange Factors affecting the rate of transpiration Plant adaptations to extreme environments Plant hormones and their commercial uses

Animal Coordination, Control and Homeostasis

Topic overview Hormones, endocrine glands and homeostasis Adrenalin, thyroxine and negative feedback The menstrual cycle and its hormones Hormonal and barrier contraception Assisted reproductive technology and IVF Homeostasis and thermoregulation Controlling blood glucose, and type 1 diabetes Type 2 diabetes and body mass The urinary system and the production of urea The nephron, filtration and the effect of ADH Treating kidney failure: dialysis and transplants

Exchange and Transport in Animals

Topic overview Why multicellular organisms need exchange surfaces Alveoli and gas exchange Rate of diffusion and Fick's law The blood and its components Arteries, veins and capillaries The heart and the circulatory system Cellular respiration as an exothermic reaction Aerobic and anaerobic respiration compared Investigating the rate of respiration Cardiac output, stroke volume and heart rate

Ecosystems and Material Cycles

Topic overview Levels of organisation and interdependence Abiotic and biotic factors in a community Parasitism and mutualism Sampling with quadrats and transects Estimating population size from field data Energy transfer between trophic levels Human impact on ecosystems and biodiversity Food security The carbon cycle The water and nitrogen cycles Indicator species and pollution Factors affecting the rate of decomposition Calculating the rate of decay

Plant Structures and Their Functions

Leaf structure for photosynthesis and gas exchange

3 things to know
Paper 2

Overview

How the broad, thin shape and large surface area to volume ratio of a leaf suit it to photosynthesis and gas exchange, the palisade and spongy mesophyll, the waxy cuticle and transparent upper epidermis, stomata on the lower surface, and the xylem and phloem in leaf veins.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Evaluation

Explain the advantage to a leaf of being thin.

Key term

Which layer of a leaf contains the most chloroplasts, and why is it positioned where it is?

Key term

Explain why the upper epidermis of a leaf is transparent.

Questions from this subtopic

Each one with the model answer underneath.

1
Explain how the broad, flat shape of a leaf suits it for photosynthesis.
Model answer
It gives a large surface area, so the leaf can absorb as much light and carbon dioxide as possible.
2
Explain the advantage to a leaf of being thin.
Model answer
Light and gases only have a short distance to travel to reach the photosynthesising cells inside.
3
Explain why a leaf with a large surface area to volume ratio exchanges gases efficiently.
Model answer
There is a lot of surface for each unit of volume, so carbon dioxide and oxygen can diffuse in and out fast enough to supply all the cells.
4
Which layer of a leaf contains the most chloroplasts, and why is it positioned where it is?
Model answer
The palisade mesophyll, which lies just below the upper surface so that its chloroplasts absorb the most light.
5
Explain the function of the air spaces in the spongy mesophyll of a leaf.
Model answer
They allow carbon dioxide to diffuse quickly to the photosynthesising cells and oxygen and water vapour to diffuse away.
6
Describe the function of the waxy cuticle on a leaf.
Model answer
It is a waterproof layer that reduces the amount of water evaporating from the leaf surface.

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Natural Selection and Genetic Modification

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ANitrates cause an algal bloom that blocks the light.

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