Chapter 5: Obtaining energy and nutrients for life

• Heterotrophs and autotrophs

• Autotrophs and photosynthesis

• Heterotrophs and food

• The digestive system

• Digestion in animals

Today’s lesson

• Heterotrophs and autotrophs

• Autotrophs and photosynthesis

Autotrophs

• Plants • Algae

• Soak up sunlight to gain energy they need for living (photosynthesis)

• Build their organic matter from simple inorganic matter taken up from their surroundings

• Terrestrial autotrophs (air and soil)• Aquatic autotrophs (water)

Autotrophs

Heterotrophs

• All animals

• All fungi

• Some bacteria

Heterotrophs

• Obtain energy for living and material for building and repairing their structure from organic matter in their surroundings

• Organic matter used by heterotroph is its food

Autotrophs and

photosynthesis

Autotrophs and photosynthesis

• Plants algae and some protists (phytoplankton) can make organic molecules (sugar) by photosynthesis

• Energy is obtained from sunlight

• Organisms that can do this are autotrophic

• Photosynthesis occurs in the chloroplasts, found in the cytosol of some cells.

Ins and outs of photosynthesis

• Sunlight is converted to chemical energy in sugars

• 2 sets of reactions

1. First set of reactions depends on the availability of light and presence of chlorophyll

2. Second set of reactions does not depend on light but depends on products from the first set of reactions

First set of reactions

Water + ADP

Sunlight

Chlorophyll

oxygen + hydrogen ions

+ ATP

ADP = Adenosine diphosphate

ATP = Adenosin triphosphate

Second set of reactions

Carbon dioxide

+ hydrogen ions

+ ATP

ADP = Adenosine diphosphate

ATP = Adenosin triphosphate

Where does Carbon dioxide come from?

Glucose + ADP

Combining the two

• ATP and ADP are used during the reactions (chemical energy)

End result:Carbon dioxide

+ water

Sunlight

ChlorophyllGlucose + oxygen

6CO2 + 6H20 C6H12O6 + 6O2

Sunlight

What makes it all happen?

• Sunlight provides the energy required to drive the first reaction

• The ATP produced from the first reaction is a high-energy compound that provides energy that drives the second set of reactions

• This leads to the production of glucose from the carbon dioxide and hydrogen ions

Plant structures in relation to photosynthesis

• Certain characteristics exist in plants which enable photosynthesis to occur

• Leaves, trunk and roots

Leaves

• Flat shape- provides large surface area exposed to sunlight

• Chloroplasts- enables it to trap energy from sunlight

• Stomata (pores) on leaf surface provide access into leaf for carbon dioxide

• Thinnes- diffusion of carbon dioxide to photosynthetic cells in the leaf tissue

• Vascular tissue and xylem vessels- transport water and other compounds

Stems

• Xylem vessels and fibres give rigidity to a stem and assist upright stance

• Branching of stems allows layers of leaves, increasing total surface area

• Xylem vessels transport water and minerals from roots to all aerial parts of plant

• Phloem transports products of photosynthesis

Roots

• Extensive root systems taps a significant volume of soil for water and mineral salts

• Root hairs- increases area available for absorption of water and mineral salts

• Oxygen from air in soil diffuses through root hairs into plants

• All the characteristics of leaves, stems and roots ensure that these structures combine to provide the sunlight energy, carbon dioxide and water that a plant requires for photosynthesis

• In other words, it enables the plant to get what it needs for the reactions to take place efficiently

Summary• Heterotrophs- all animals, fungi, bacteria• Autotrophs- all plants, algae, some bacteria• Autotrophs make their own organic material from

inorganic substances (using sunlight)• Heterotrophs rely on food, organic matter • Photosynthesis- converting energy of sunlight to

chemical energy in sugars• Raw materials of photosynthesis are carbon

dioxide and water, products are sugar and O2

• Structures of various parts of plants maximise plant’s ability to obtain raw materials necessary for photosynthesis