Unit 1; Area of Study 2

Functioning Organisms

Chapter 5

Obtaining Energy and Nutrients for Life

WEEK 6: Obtaining NutrientsLEARNING OUTCOMESBy 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 photosynthesisLEARNING OUTCOMESBy 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 What do the terms mean? Watch the clip....

Is the whale shark an active feeder or a passive feeder?

Heterotrophs 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 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 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 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?

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 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 EquationWord equation:

Balanced chemical symbol equation:

lightchlorophyll

lightchlorophyll

carbon dioxide+ water glucose+ oxygen

6CO2+ 6H2O C6H12O6+ 6O2

Or: six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.

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 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:

Upper epidermis Palisade layer Spongy layer Lower epidermis

Mesophyll layer

Inside the leaf

Structure of the Leaf

Waxy cuticle Vein/vascular bundle Air space Stoma Guard cell

Upper epidermis Lower epidermis Palisade cell Spongy mesophyll cell

Label the diagram with the structures:

Waxy cuticle

Upper epidermis

Palisade cell

Spongy mesophyll cell

Air spaceLower epidermis

Guard cellStoma

Vascular bundle (vein) – xylem and phloem

AB

C

D

E

F

GHI

Epidermis Single layer of cells on the upper and lower

surfaces of the leaf. Helps to keep the leaf’s shape. Has closely fitting cells:

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 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. 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 ofSPONGY MESOPHYLL CELLS Vary in shape, and fit loosely together. Many air spaces between them.

chloroplasts.

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) 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.