Plants -All life on Earth depends on billions of tiny reactions in billions of tiny, green cells. RetsimNesmoht
Plant Evolution. • Ancestors began in the water. • Over time, the demands of life on land favored the evolution of plants more resistant to the drying rays of the sun, more capable of conserving water, and more capable of reproducing without water.
Seed PlantsGymnosperms (cones) & Angiosperms (flowers) • The evolution of seeds allowed plants to reproduce without standing water. • It includes a reproductive process that takes place in cones or flowers. • It includes the transfer of sperm by pollination. • It includes the protection of the embryo in seeds
Photosynthesis • Photosynthesis involves the use of solar energy to produce food (Glucose). • The leaf is the plant structure designed to capture the Sun’s energy. • The outer layer is called the epidermis. • There can be a coat of wax on the epidermis called the cuticle
Cuticle • Functions of the cuticle: • Protect the leaf from attack, (bacteria, fungi, insects). • Keep water from escaping from the leaf. • Always found on the top surface. • Thicker, and on the bottom surface of some leaves. Especially leaves in drier climates.
Inner layers of a leaf • The Palisade layer is where most photosynthesis takes place. • The Spongy layer is more important for gas exchange. • The exchange of gases and water occurs through the stoma. • The size of the stomates are controlled by guard cells.
Chloroplasts • Located in the palisade and spongy cells. • This is the site of photosynthesis. • It is a double-membraned organelle. • Inner fluid is the stroma • Inside the stroma are flattened membrane structures called thylakoids.
Thylakoids • Flattened membrane structures inside the stroma. • Thylakoids are stacked into structures called grana. • The membranes of the thylakoids are filled with chlorophyll
Photosynthesis • Respiration (what animals do) • C6H12O6 + 6O2 = 6CO2 + 6HOH + energy • Photosynthesis (what green plants do) • 6CO2 + 6HOH + solar energy = C6H12O6+ 6O2 • Two main groups of photosynthesis: light-dependent reactions and light independent reactions.
Light dependent photosynthesis • Converts solar energy into usable energy for the plant, NADPH and ATP. • The reactions occur along the thylakoid membranes. • Chlorophyll provides the energy from sunlight. • Oxygen is released as a by-product.
Electron Carriers in the light dependent reaction • Chlorophyll absorbs the sun’s energy and transfers that energy to electrons. • The energy in these electrons is stored in NADP+ forming NADPH. • The absorbed energy in chlorophyll is also used to split water into H+ and O. • The H+ is used to make ATP. • The O2 is released as a waste.
Light-independent reactions (Calvin Cycle) • These reactions take place in the stroma of the chloroplast. • They rely on the energy (ATP and NADPH) from the light-dependent reactions in order to run. • Their product is a three carbon carbohydrate called glyceraldehyde-3-phosphate (G3P) which can be used to form glucose and other carbohydrates
Plant Transport • Plants must move water and minerals to the leaves. • Plants must move nutrients, from photosynthesis, from the leaves to the rest of the plant. • Water and nutrients are carried in specific vessels within veins called xylem and phloem
Roots and xylem • Root hairs absorb water and minerals from the soil. • These are transported through xylem tissue upward to the rest of the plant. • The specific cells that transport water are called tracheids and vessel elements.
Tracheids and vessel elements are dead, hollow cells specialized to conduct water from the root.
Phloem • Food from photosynthesis is transported through the plant by phloem. • Phloem contains two types of cells: sieve cells and companion cells. • Sieve cells do the actual transport and the companion cells help the sieve cells with their metabolic functions.
Xylem and phloem in a tree trunk.The xylem layer is dead.The cambium is composed of stem cells that become bark, xylem and phloem
Flowers and reproduction • Flowering plants are called angiosperms. • The flower is the reproductive organ of flowering plants. • The 2 most important parts of the flower are the stamens and the Pistil.
The Stamen • The stamen is the plant’s male component. • It consists of the anther and the filament. • The anther makes pollen. • Pollen is made from little cells called microspores. • Mature pollen grains contain a cell that can divide to form two sperm cells.
The Pistil • The pistil is the female part of the flower. • It consists of the stigma, style, ovule and ovary. • Inside the ovary is the ovule which forms cells called megaspores. • Megaspores can divide to form eggs and polar bodies.
Plant Reproduction with flowers • Pollen grains fall on stigma • Pollen germinates and pollen tube grows through the style into the ovary. • Two sperm enter the ovary and one fertilizes the egg and the other combines with the polar bodies. • The fertilized egg becomes the plant embryo. (2N) • The polar bodies become the endosperm (3N).
Seed development • The entire ovule, embryo and endosperm develops into a seed. • The endosperm becomes a food-storing tissue that surrounds embryo. • The ovary develops into a fruit. • The fruit protects the seed and helps it disperse by wind or animals.
Seed Viability • Most seeds stay viable for 2 – 10 years. • Recently some seeds from an ancient arctic ground squirrel burrow were planted and germinated. • The frozen seeds were 32,000 years old! • The plant was the narrow-leafed campion.