Edexcel SNAB AS Biology Topic 1: heart and circulation

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Edexcel SNAB AS Biology

Topic 1, Unit 1- Why have a heart and circulation?

INTRODUCTION

Small organisms have a LARGE SURFACE AREA VOLUME RATIO and a LOW METABOLIC RATE.

Simple DIFFUSION is effective to move substances such as OXYGEN, CARBON DIOXIDE and DIGESTIVE PRODUCTS around their bodies.

For complexed multicellular organisms with a SMALL SURFACE AREA VOLUME RATIO and a HIGH METABOLIC RATE diffusion is not sufficient for meeting their needs. Therefore they require a CIRCULATORY SYSTEM and HEART.

PAST EXAM QUESTIONS

Explain why a pig has a heart and circulation whereas a flatworm does not.

Flatworms have a large surface area to volume ration.

Diffusion is sufficient to meet their needs.

A pig has a higher metabolic rate which means that diffusion is not suitable

Suggest the advantages of DOUBLE CIRCULATION.

Allows blood to the lungs to flow at lower pressure.

This means that there is less risk of damage to the lungs.

Blood coming from the lungs results in a loss of pressure.

Pumping the blood again provides it with an extra boost to restore the lost pressure.

Blood flows at a higher pressure to the body.

More effective transport and exchange of gases.

Suggest why an insect doesn't need blood vessels to transport blood around its body. (OPEN CIRCULATORY SYSTEM)

Large surface area to volume ratio.

Therefore all cells are found close to the blood/circulation.

Low metabolic rate.

Diffusion fast enough for exchange of nutrients/gases/waste.

CLOSED CIRCULATORY SYSTEM...

Blood flows enclosed in tubes.

Generates higher blood pressure as blood is forced along narrow channels.

Blood travels faster.

More effective.

What is a major disadvantage of a THREE CHAMBERED HEART, as is found in amphibians?

Oxygenated and deoxygenated blood mix.