How do the nutrients in dead matter become available to leaves?

When something, whether its animals or plants dies, they are broken down by microorganisms (decomposers). These microorganisms are also called saprobionts. These secrete enzymes onto dead tissue, this is called extracellular digestion. They absorb products of digestion. Respiration by microorganisms produces carbon dioxide. Carbon dioxide is then taken into the leaves.

How can Global Warming effect crop yield?

Global warming is caused by an increase in carbon dioxide - so weirdly, global warming is kind of increasing our crop yields. This is because carbon dioxide is a limiting factor for photosynthesis, so if you increase the amount of carbon dioxide then you increase the amount of photosynthesis which can take place. More photosynthesis means a faster growth rate, more crops and a higher yield. 

What is the carbon cycle?

Carbon dioxide, or CO2 (excuse the missing subscript) is all around us, mainly in the air and water. Plants remove carbon dioxide from the atmosphere as they carry out photosynthesis. Once the carbon dioxide has entered the plant, it becomes carbon compounds within the plant tissues.

Plants are then eaten by animals (the primary consumers) - the carbon is passed on to those animals. It then gets passed on to each successive consumer. Of course, at some point, all of these organisms die - they leave behind carbon compounds in them. Microorganisms called decomposers then digest these carbon compounds. As they feed on dead organic matter, this is called saprobiontic nutrition.

The cycle continues as the carbon is returned to the air and water due to respiration. During respiration, carbon dioxide is released into the atmosphere.

There are times where carbon compounds end up where there's not decomposers - this might be deep oceans or bogs. This means that over millions of years, they are turned into fossil fuels by heat and pressure. When fossil fuels are burnt, the carbon is released - you might know this as combustion.

Movement of Blood around the Body | AS Level Biology Revision

Arteries:

AWAY from the Heart

to Arterioles

Veins:

BACK to the Heart

Link Arterioles to Veins - CAPILLARIES (tiny vessels)

Arterioles - small arteries

Control blood flow into the capillaries

Path (starting going AWAY from the heart)

• Arteries
• Arterioles
• Capillaries
• Veins
• Heart 

Try this mnemonic to help remember the order:

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