Photosynthesis and Leaves Photosynthesis process used by plants

Photosynthesis and Leaves

Photosynthesis • process used by plants using light energy to create sugar (glucose, C 6 H 12 O 6) from carbon dioxide (CO 2) and water (H 2 O) • oxygen gas (O 2) is produced as a waste product and the light energy used is stored as chemical energy

Investigating Photosynthesis • Jan Van Helmont (1643) – Carefully massed soil, and tree seedling and watered over 5 years. – Determined most of the mass of the tree came from water.

Investigating Photosynthesis • Joseph Priestley (1771) – Lit a candle and placed a bell jar over it, watching the flame go out. – Reasoned that there was something in the air necessary to keep the flame going. – When a plant was placed under the bell jar, discovered that the candle could be relit after several days. – Reasoned that the plant released something into the air necessary for the flame.

Investigating Photosynthesis • Jan Ingenhousz (1779) – Showed the effect observed by Priestley only occurred when plants were exposed to light.

Investigating Photosynthesis • Julius Robert Mayer (1845) – Proposed that plants convert light energy into chemical energy

Photosynthesis Equation

Chloroplast • oval shaped organelle in plant leaf cells (and some protists’ cells) where photosynthesis takes place

Light • plants use visible light to power photosynthesis in chloroplasts – visible (white) light is actually ALL visible colors of light – plants absorb energy from many different colors of light

Pigment • material that changes the color of reflected light • plants gather the sun’s energy with light absorbing pigments

Pigment • the primary plant pigment is chlorophyll

Chlorophyll • plant pigment that absorbs light energy very well in the blue, violet and red wavelengths of visible light • Why are plants green? – chlorophyll reflects green light

Carotenoids • secondary pigments • absorb different wavelengths of light – produces fall leaf colors as plants break down chlorophyll – produces colors of many fruits and vegetables

Leaves • organs where photosynthesis takes place • provide a place for gas exchange

Stomata • pores on the surface of a leaf • allow gases to enter and leave the plant • surrounded by two guard cells

Guard Cells • specialized cells that can open and close to control gas exchange • typically closed in time of drought – prevents water from leaving the plant

Mesophyll • chlorophyll containing leaf tissue • portion of the leaf that conducts photosynthesis

Mesophyll – palisade mesophyll • dense area of sugar-producing cells

Mesophyll – spongy mesophyll • area of sugar-producing cells with many air spaces

Cuticle • waxy outside layer of a leaf – helps prevent water loss

Epidermis • outside layer of cells

Xylem and Phloem • vascular bundle (______) of the plant

Xylem and Phloem • vascular bundle (veins) of the plant – xylem – moves water and minerals

Xylem and Phloem • vascular bundle (veins) of the plant – phloem – moves food energy (sugar)

Xylem and Phloem

Summary Using whiteboards, identify the letter labels below. C B D E F&G A H I J

Summary Label the following leaf cross section.

Factors that affect Photosynthesis *think of the “ingredients” necessary for photosynthesis* • characteristics of the ecosystem that a plant grows in can affect how well it can perform photosynthesis – some factors allow plants to make sugar quickly while other factors slow down their ability to make sugar • light – length of exposure, color, intensity or brightness (distance from source) • water amounts • CO 2 concentration

Photosynthesis and Enzymes • plants use many enzymes to produce their food made in the process of photosynthesis – enzymes are proteins that speed up chemical reactions • enzyme efficiency can be affected by many factors – Temperature, p. H • these factors can also speed up (or slow down) photosynthesis

Connection to ATP • But what do living things do with the sugar made in photosynthesis? – Eventually…living things will break down sugar and convert the energy into ATP – More on this later when we learn about cellular respiration

Summary • Sometimes plants in a community will slow down or stop performing photosynthesis. This can be brought on by drought, human activities, disease, or many other factors. Describe what would happen to other members of the plants’ community.