Unit 1; Area of Study 2
Functioning Organisms
Chapter 5
Obtaining Energy and Nutrients for Life
WEEK 6: Obtaining
Nutrients
LEARNING OUTCOMES
By the end of this week, you should be able to explain:
 Biochemical processes including photosynthesis and
cellular respiration in terms of inputs and outputs.
 Obtaining nutrients: organic and inorganic requirements;
autotrophs; heterotrophs.
 Obtaining energy: inputs and outputs of photosynthesis;
structural features of photosynthetic organisms.
 Processing nutrients: features of effective systems in
heterotrophs; examples of systems in different animals.
LESSON 1: Heterotrophs,
autotrophs and photosynthesis
LEARNING OUTCOMES
By the end of this lesson, you should be able to:
 Define ‘autotroph’ and ‘heterotroph’.
 Distinguish between heterotrophs and autotrophs in
terms of nutrient requirements for life.
 Summarise the process of photosynthesis in a word
equation and chemical equation.
 Identify structural features of photosynthetic organisms
that facilitate their ability to photosynthesise.
Active and Passive
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What do the terms mean?
Watch the clip....
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Is the whale shark an active feeder or a passive
feeder?
Heterotrophs
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Actively obtain the energy they need for life by
feeding on organic matter found in their
surroundings (food!)
They then use this organic matter to build and
repair their cells.
Give some examples...
What structural, physiological and behavioural
adaptations do heterotrophs have to help them
obtain their food?
Autotrophs
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Organisms that just take up (absorb) the energy
they need from their surroundings.
They build organic matter from simple inorganic
matter taken up from the air, soil or water.
Give some examples.....
So what about these guys...?
Carnivorous Plants
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Carnivorous plants still need water and
sunlight like other green plants to make
food/energy (glucose) but they get their
mineral nutrients from trapping and consuming
animals.
Carnivorous plants are adapted to grow in
places where the soil is thin or lacking
nutrients, especially nitrogen, such as
acidic bogs and rock outcroppings.
Photosynthesis

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Plants, algae and some
protists can make
sugars by
photosynthesis.
Sunlight energy is
converted into
chemical energy (in
the form of glucose)
in the chloroplasts
found in the cytosol of
cells.
What do you know already?
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Plants use the energy
from the sun to make
molecules such as
glucose, starch and
proteins.
These molecules can
then be used for food
for the plant, but also
for animals like us.
A waste product of
the process is oxygen,
which is released into
the atmosphere.
The Importance

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The importance of photosynthesis is in the
conversion of unusable sunlight energy into
usable chemical energy (glucose).
It is one of the most important biochemical
processes, since nearly all life on Earth either
directly or indirectly depends on it as a source
of energy.
The Equation
Word equation:
carbon dioxide
+ water
light
chlorophyll
glucose+ oxygen
Balanced chemical symbol equation:
6CO2+ 6H2O
light
chlorophyll
C6H12O6+ 6O2

Or: six molecules of water plus six molecules
of carbon dioxide produce one molecule of
sugar plus six molecules of oxygen.
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Plants absorb water
through their roots,
and carbon dioxide
through their leaves.
Some glucose is used
for respiration, while
some is converted into
insoluble starch for
storage.
The stored starch can
later be turned back
into glucose and used
in respiration.
Testing a green leaf for starch

Will a plant that has been kept in a dark cupboard
for a few days contain starch in its leaves?
Structure of the Leaf

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Photosynthesis takes place mainly in the cells of
the leaves.
Leaves are well adapted for photosynthesis – its
structure is well suited to its function.
Leaves are made up of four main layers:

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Upper epidermis
Palisade layer
Spongy layer
Lower epidermis
Mesophyll layer
Inside the leaf
Structure of the Leaf
Label the diagram with the structures:
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Waxy cuticle
Vein/vascular bundle
Air space
Stoma
Guard cell
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Upper epidermis
Lower epidermis
Palisade cell
Spongy mesophyll cell
Waxy cuticle
Vascular bundle (vein) – xylem and phloem
Upper
epidermis
Palisade cell
Spongy
mesophyll cell
Air space
Lower
epidermis
Stoma
Guard cell
A
B
C
D
E
F
I
H
G
Epidermis
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Single layer of cells on the upper and lower
surfaces of the leaf.
Helps to keep the leaf’s shape.
Has closely fitting cells:
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Reduces evaporation from the leaf
Prevents bacteria and fungi from getting in
Thin waxy layer covering epidermis called the
cuticle – helps to reduce water loss further.
Have stomata.
In woody stems, the epidermis is bark.
Stomata
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Singular: stoma
Structures in the leaf epidermis.
Consists of a pair of guard cells, surrounding
an opening called the stomatal pore.
The stomata can open and close by changes in
the turgor and shape of the guard cells.
In some plants they are located on the lower
epidermis only, others have stomata on both
sides of the leaf.
Stoma
Guard cell
Leaf epidermal cell
How Do Stomata Work?

Generally, they open during daylight hours
(whilst photosynthesis is taking place) and
close during the night.
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Why?
What do plants need to photosynthesise?
During the day they are open to allow carbon
dioxide to diffuse into the leaf (and oxygen
out) so photosynthesis can take place.
Mesophyll
Tissue between the upper and lower epidermis.
 Consists of two layers (see diagram).
PALISADE CELLS:
 Function – to make food by photosynthesis.
 Hence, they have lots of
SPONGY MESOPHYLLchloroplasts.
CELLS
 Vary in shape, and fit loosely together.
 Many air spaces between them.

Air Spaces

Whilst photosynthesis is taking place, the air
spaces in the mesophyll layer fill with carbon
dioxide as it enters the leaf, and oxygen as it
leaves the leaf.
Veins (vascular bundles)
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Xylem vessels carriy water needed for
photosynthesis to the mesophyll cells.
The mesophyll cells take in water through
osmosis.
Branching network – no cell is far away from a
water supply.
Sugars made in mesophyll cells are passed to
the phloem cells – carry sugar away from the
leaf to the stem.