Organic substances decay into simpler substances.
The leaves fall off many trees in autumn.
from
in from the atmosphe
fuels offer the organisme d
puried by layers of sediment. Over millions of years, they
, plankton and marine animals dis, they fell to
and form gedimentary rocks, oil and gas-trapping the co
and helping to keep carbon dioxide levels in the atmospher
Things like coal, crude oil and
gas that are made by
Do not write
outside the
bex
om deposits of plank
get trapped in rocks
hick plant deposits.
Y'a mostly made of
f marine organisms.
The dead leaves contain carbon compounds and nitrogen compounds.
Describe how carbon and nitrogen in compounds in the leaves are recycled and used
by living trees.
You should include a description of:
how the leaves are broken down
how substances are taken in and used by the trees.
[6 marks]

**Organic substances decay into simpler substances.** This process is essential for nutrient cycling in the environment. For example, **the leaves that fall off many trees in autumn** eventually decompose through the action of bacteria and fungi. These decomposers break down the complex organic material in the leaves into simpler nutrients that can be reused by plants.

**Fossil fuels** like coal, crude oil, and natural gas are also formed from organic materials. Millions of years ago, dead plants and marine animals accumulated in layers under pressure and without oxygen. Over time, heat and pressure transformed these buried remains into the fossil fuels we use today.

**Fossil fuels offer the organisms that use them a concentrated source of energy**. However, when burned, they release carbon dioxide, a greenhouse gas, back into the atmosphere. This can contribute to climate change.

**Sedimentary rocks can trap pockets of oil and gas**. These resources are formed from the remains of plankton and other marine organisms that died and settled on the ocean floor. Over millions of years, these layers were buried and compressed, forming oil and gas deposits.