Photosynthesis

Photosynthesis

• What is it?
• Photosynthesis is a chemical process through which plants, some bacteria and algae, produce glucose and oxygen from carbon dioxide and water, using only light as a source of energy.
• During
• photosynthesis radiant energy from the sun (sunlight) is absorbed by
• green plants. The energy is used to convert carbon dioxide, water and
• minerals the plants take in from their surroundings into sugar and
• gaseous oxygen.
• Photosynthesis
• is critical to life on Earth. Without photosynthesis the food supply
• would finish and the Earth’s atmosphere would lose its oxygen.
• 
• Caption: The Process of Photosynthesis in Plants

The 2 Stages of Photosynthesis

• The photochemical stage involves the radiant energy supplied by
• sunlight and involves reactions called light dependant reactions. Green
• plants contain a light absorbing pigment called chlorophyll. When a
• molecule of chlorophyll absorbs light it uses the energy to boost
• electrons to a higher energy level and the molecule is said to be
• excited. The electrons at the higher energy levels are transferred along
• chains of electron carrier molecules. The energy transfers of the
• electrons are responsible for the formation of key energy carrying
• molecules along with the splitting of the water molecule to oxygen and
• hydrogen.
• These molecules then undergo the second stage of
• photosynthesis, the biochemical reaction. Here they react with hydrogen
• formed from the splitting of water in the photochemical stage and carbon
• dioxide from the atmosphere with the presence of enzymes to form the
• organic glucose molecules. The reactions in this stage are referred to
• as light-independent reactions because they do not require light as they
• use the energy already provided by the light in the light-dependent
• reactions. Thus, photosynthesis has transferred the energy from light to
• chemical energy in the sugar.

Factors Limiting Photosynthesis

• Photosynthesis can be limited by three factors: light intensity, carbon dioxide concentration and temperature.
• Without enough light, a plant cannot photosynthesise very quickly, even
• if there is plenty of water and carbon dioxide. Increasing the light
• intensity will boost the speed of photosynthesis.
• Sometimes photosynthesis is limited by the concentration of carbon
• dioxide in the air. Even if there is plenty of light, a plant cannot
• photosynthesise if there is insufficient carbon dioxide.
• If it gets too cold, the rate of photosynthesis will decrease. Plants
• cannot photosynthesise if it gets too hot.If you plot the rate of
• photosynthesis against the levels of these three limiting factors, you
• get graphs like the ones above.
• The Rate of Photosynthesis
• Plants and photosynthesis

Photosynthesis and Transportation

• https://www.youtube.com/watch?v=cMte2VCtZ-I (Embed)
• Caption: Process of photosynthesis and transportation of material in plants