Plant Processes Chapter 12

The Reproduction of Flowering Plants Section 1 The Reproduction of Flowering Plants Flowering plants are the largest & most divers group of plants in the world. Their success is partly due to their flowers, which are adaptations for sexual reproduction. During sexual reproduction, an egg is fertilized by a sperm cell. In flowering plants, fertilization takes place within the flower & leads to the formation of one or more seeds within a fruit.

How Does Fertilization Occur? Section 1 How Does Fertilization Occur? Fertilization For Flowering Plants Start of fertilization: When pollen grains are transported from anthers to stigmas. After pollen lands on the stigma, a tube grows from the pollen grain through the style to the ovary. Sperm cells within pollen grain move down the pollen tube & into an ovule. Fertilization occurs as one of the sperm cells fuses with the egg inside the ovule. Sperm cells inside pollen grains. Ovules are inside the ovary and an egg is inside each ovules

Section 1 From Flower to Fruit After fertilization takes place, the ovule develops into a seed that contains a tiny, undeveloped plant. The ovary surrounding the ovule develops into a fruit. As the fruit swells & ripens, it holds & protects the developing seeds. Petals & stamens fall away.

Seeds Become New Plants Section 1 Seeds Become New Plants When a seed is fully developed The young plant inside stops growing It may become dormant Dormant = alive but temporarily inactive When dormant it can survive long periods of drought or freezing temperatures. Some seeds need extreme conditions such as cold winters or forest fires to break their dormancy. When planted in an area that has water, oxygen, & suitable temperatures, it germinates (or begins to grow)

Section 1 Other Methods Many flowering plants can also reproduce asexually. Asexual reproduction in plants does not involve the formation of flowers, seeds, & fruits. In asexual reproduction, a part of a plant, such as a stem or root, produces a new plant.

Other Methods Examples Section 1 Other Methods Examples Potato tubers are underground stems that are swollen with stored food. The “eyes” of potatoes are buds that can grow asexually into new plants The strawberry plant produces runners, which are stems that run horizontally along the ground. Buds along each runner grow into new plants that root in the ground. The kalanchoe plant produces plantlets, tiny plants along the margins of its leaves. The young plantlets eventually fall off the mother plant & root in the soil as separate plants.

The Ins & Outs of Making Food Section 2 The Ins & Outs of Making Food Plants do not have lungs, but they need air just like you. Air is a mixture of oxygen, carbon dioxide, & other gases. Plants must have carbon dioxide to carry out photosynthesis, which is the way they make their own food.

What Happens During Photosynthesis? Section 2 What Happens During Photosynthesis? Plants need sunlight to produce food. During photosynthesis, the energy in sunlight is used to make food in the form of sugar (C6H12O6) from carbon dioxide (CO2) & water (H2O). How does this happen?

Capturing Light Energy Section 2 Capturing Light Energy Plant cells have organelles called chloroplasts. Chloroplasts contain chlorophyll. Chlorophyll = a green pigment that absorb light energy. Sunlight is a mixture of all the colors of the rainbow. Chlorophyll absorbs most of the colors in light, but not green. Plants look green because chlorophyll reflects green light.

Section 2 Making Sugar The light energy absorbed by chlorophyll is used to split water (H2O) into hydrogen (H) & oxygen (O). The hydrogen is then combined with carbon dioxide (CO2) from the air surrounding the plant to make sugar (C6H12O6). Oxygen is given off as a byproduct. There process of photosynthesis is summarized in the following chemical equation: The equation shows that it takes six molecules of carbon dioxide & six molecules of water to produce one molecule of glucose & six molecules of oxygen. light energy 6CO2 + 6H2O C6H12O6 + 6O2

Section 2 Making Sugar Cont. The energy stored in food molecules is used by plant cells to carry out their life processes. Within each living cell, sugar & other food molecules are broken down in a process call cellular respiration. Cellular respiration = coverts the energy stored in food into a form of energy that cells can use. During this process, the plant uses oxygen & releases carbon dioxide & water.

Section 2 Gas Exchange cuticle = a waxy layer that doesn’t allow gases or water to pass through. It covers all aboveground plant surfaces. Stomata = an opening in the leaf’s epidermis & cuticle. Each stoma is surrounded by two guard cells, which act like double doors opening & closing the gap. Transpiration = when water vaper exits the leaf through the stomata How does a plant obtain carbon dioxide through this barrier? CO2 enters the leaf & diffuses into the leaf cells & O2 diffuses out of the leaf’s cells & exits the leaf When a plant wilts, it is usually because more water is being lost through its leaves than is being absorbed by its roots.

Section 3 Plant Tropisms Tropism = growth in response to stimulus (can be positive [plant grows towards stimulus] or negative [plant grows away from the stimulus) Sensing light – Phototropism = a change in the growth of a plant that is caused by light. (positive) Which Way is Up? Gravitropism = when the growth of a plant changes direction in response to the direction of gravity. (the plant negative while the roots are positive) Plants respond to environmental stimuli, such as light, gravity, changing seasons, and even being eaten.

As Different as Night & Day Section 3 As Different as Night & Day As autumn & winter approach, the days get shorter & nights get longer. The opposite happens when spring & summer approach. This difference in the length of day & night is an important environmental stimulus for many plants. Short-day plants: plants that bloom in autumn. Poinsettias, ragweed, & chrysanthemums Long-day plants: plants that bloom in spring or early summer. Clover, spinach & lettuce

Seasonal Changes in Leaves Section 3 Seasonal Changes in Leaves Evergreen = have leaves adapted to survive throughout the year. Deciduous = lose all their leaves at the same time each year. Having bare branches during the winter or dry season reduces the water lost by transpiration. As autumn approaches, chlorophyll, the green pigment used in photosynthesis, breaks down. As chlorophyll is lost from leaves, other pigments are revealed. (like red, yellow, or orange)

Section 4 Plant Growth Heredity A plant’s traits, such as heart-shaped leaves or red flowers, are determined mainly by the plant’s genes, or its DNA. Environment A plant’s behavior & appearance can be affected by the plant's environment. The amount of daylight, darkness, water, and the kind of soil are just a few of many environmental factors that can affect the plant’s growth.

Section 4 Plant Hormones Heredity & environment affect a plant’s production of hormones. Hormones = chemical messengers that carry information from one part of an organism to another. They are produced in small amounts, but they have a strong effect on the organism. Auxin – a hormone produced in shoot tips, has many effects on plant growth. (phototropism) Gibberellin – affects plant growth. (makes the plant grow tall & bear more fruit)