THE HUMAN BODY
Part A: Digestion and Nutrition
V.C.E. BIOLOGY UNIT 1
Autotrophs are producers
Requirements of Living Things
• Energy – all life requires a source of energy
• Oxygen – organisms require oxygen for cellular
respiration
• Water – required for growth, maintenance and
repair
• Nutrients – required for growth, maintenance and
repair
• Waste removal – many harmful by-products result
from the cells chemical processes
• Reproduction – organisms need to replace
themselves
Autotrophs and Heterotrophs
• Autotrophs are organisms that are able to make their own
organic molecules they need from simple inorganic
molecules – they are self feeders.
• Heterotrophs are unable to synthesise their own organic
molecules, they must eat other living things.
Autotrophs
• Most autotrophs are plants that create organic molecules
(glucose) through a process known as photosynthesis
which occurs in specialised cell organelles called
chloroplasts.
• Some bacteria are able to produce organic molecules
from inorganic molecules in a process called
chemosynthesis.
Photosynthesis
• Plants make the organic material, glucose, from simple
inorganic molecules, carbon dioxide and water, in the
presence of light energy and chlorophyll. This allows for
the conversion of light energy into stored chemical energy
for use by the plant.
Light energy
6CO2 + 12H20  C6H12O6 + 6H20 + 6O2
chlorophyll
Photosynthesis/Cellular Respiration
• Autotrophs use energy twenty four hours a day –
using oxygen to break down glucose to release
the energy and produce water and carbon
dioxide.
• By day this is balanced by the photosynthesise
that occurs – using carbon dioxide and water to
produce glucose and oxygen.
• At low light levels the plant must take up oxygen
for cellular respiration, but at higher light levels
the plant produces excess oxygen through
photosynthesis.
Structural Adaptations
• Plants have evolved many adaptations to collect
light more efficiently.
• Obviously leaves at the end of stems and
branches allows the plant to collect more light
than merely growing along the ground.
• Dorsiventral leaves – one side has all the
chlorophyll containing cells the other has none or
few.
• Isobilateral leaves – hang vertically reducing heat
absorption, but chlorophyll is present on both
sides of the leaf
Other Nutritional Requirements
• Plants need other nutrients also. Just like animals
they need to be able to make lipid based
membranes and nitrogen based proteins and
hormones.
• Nitrogen is abundant on Earth, but mostly found
in the atmosphere in a form that organisms can’t
use. Many plants have formed symbiotic
relationships with bacteria that live in the roots
and convert the nitrogen into a useable form.
Other Nutritional Requirements
• Mineral Salts.
Plants need elements such as nitrogen,
phosphorous, potassium, sulfur, calcium and
magnesium in large quantities for making
proteins and many cell processes. These are
called the macronutrients.
They also need micronutrients such as iron, boron
and zinc in small amounts.
These are drawn up from the soil by the roots
V.C.E. BIOLOGY UNIT 1
Heterotrophs are consumers
Nutritional Requirements
• Carbohydrates – an immediate source of energy and can
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be used to store energy as glycogen.
Lipids – also an energy source and store (adipose cells)
important for membranes, hormones and vitamins.
Proteins – cells need amino acids to make proteins. There
are nine essential amino acids that must be in an animals
diet.
Vitamins – vitamins are a diverse group of organic
compounds which are used in a broad range of chemical
processes in the cell.
Minerals – these are the mineral salts or metal salts that
are important for making new cells, particularly blood cells
and to aid other processes.
Digestion
Food must be digested by heterotrophs.
• Chemical digestion is the use of chemicals called
enzymes to break large molecules into smaller
ones for absorption into the blood vessels
• Physical digestion is the use of teeth, specialised
bones, tongue and muscles to mechanically
break down large chunks of food into smaller
chunks – increasing the surface area to volume
ration for the enzymes to work.
Digestive Systems
• The simplest heterotrophs absorb their nutrients
from their surroundings by diffusion.
• As organisms become more complex they need
to eat food, digest it and send the chemicals
around the body for each cell to use. Therefore
systems of specialised organs evolved. Each
system suits the organisms diet.
• Systems contain features for mechanical
digestion, a one way flow, sequential release of
enzymes, improved surface areas for uptake of
nutrients and efficient excretion of wastes.
Mammalian Digestive Systems
• There is much variation between mammals, however,
they all contain:
A mouth cavity (may have teeth and tongue) – initial
physical and chemical digestion (uptake of glucose)
Oesphagus – physical digestion
Stomach – physical digestion and chemical digestion
(break down of fats and proteins)
Small Intestine (villi and microvilli) – chemical digestion –
major site of absorption of lipids, proteins and
carbohydrates
Large Intestine – final chemical digestion (salts absorbed)
and uptake of water
Rectum – excretes waste material.
Energy Storage
• All animals will feast when food is plentiful and store the
excess energy for times of famine as this is a natural
cycle.
• Humans have broken free of this cycle and need to be
sure that they do not regularly eat more energy than they
are using or they will store excess energy – which may
cause medical concerns.
• Animals store excess energy as fat because it is lighter
than carbohydrates (50%), contains more ATP (25%) and
can therefore yield more energy for the animal.
• Excess energy is initially stored in the liver and high
energy use areas as glycogen (cho), but if there is more
excess then lipids are deposited in adipose tissue around
organs and about the body.