Plant+Chapter!

= Plants! =


 * Systems: ** Systems are complex collections of parts that interact to produce a result. Systems require energy and matter and are made up of levels that are highly organized and complex. Physical systems must receive energy and matter in order to maintain the system. There are living and non-living systems...how can you tell the difference?

__Characteristics of Life__ **A Common Misconception About Life:** The way to tell if something is living is if it breathes or not. **The Truth:** There are six traits that living organisms have that show that they are living! These characteristics are: (Belk & Maier 1210).
 * Growth
 * Movement
 * Reproduction
 * Response to external environment
 * Metabolism
 * This is all the chemical processes that occur in cells, specifically the breakdown of food and transforming it into energy.
 * Maintain Homeostasis
 * This means the organism can maintain a stable internal environment even though the external environment is always changing.


 * Cell Function: ** [[image:elodeacell.jpg width="172" height="205"]] What exactly is a cell? Cells are the starting point for anything that is living. They contain DNA and are the most minuscule unit of life. All living systems needing matter and energy are made of cells. Cells can be complex and highly organized because they hold all of the biological equipment required to keep an organism alive and flourishing on Earth. A cells main purpose is to organize. A cell can be a single organism in and of itself, but they occur in multiples in plants. These collections of multiple cells are what form tissues. The mitochondria and chloroplasts produce Adenosine Triphosphate (ATP). ATP is the means through which energy is circulated in and among cells and is the most common energy carrier. ATP is a nucleotide made up of adenine, the sugar ribose, and three phosphate groups. It is a high-energy molecule that is used for energy storage. ATP is made during photosynthesis.

**A Common Misconception About Cells:** Every living organism is made up of the same kind of cell. **The Truth:** Cells are divided into 2 groups: Plant Cells and Animal Cells. Structurally, plant and animal cells are very similar because they are both eukaryotic cells and contain similar **cell membranes**. Besides a plant cell being bigger than an animal cell and both cells containing a **nucleus**, there are three key structures in a plant cell that distinguish it from an animal cell. (Chiras, 1993).
 * **The Cell Wall** is composed of cellulose that provide stability, structure and protection to the plant cell. The cell wall limit’s the cells flexibility. It has a rigid outer covering on the outside of the cell membrane. One disadvantage of the cell wall is that it limit’s the water uptake. The cell wall bonds with other cell walls to form the structure of the plant.
 * ** The Central Vacuole ** stores water levels and minerals that help the plant with digestion. Vacuoles are large, liquid-filled organelles that are only found in plant cells. The central vacuole also breaks down waste products, balances cell pH, and is very prominent within the cell (some can take up 90% of cell volume!)
 * **The Chloroplasts** help the plant with photosynthesis. In animal cells, the mitochondria produce the majority of the cells energy from food. In plants, sunlight is the essential energy source and the sunlight is converted into energy inside the cell through the process of photosynthesis. Chloroplasts are the structures that perform this function. They also contain chlorophyll, which absorbs the sunlight and allows us to see the green plant.



One thing that plants have an advantage over animals when it comes to imbalances of solute in water, is their cell wall. Remember the cell wall is very strong and rigid to help protect the cell, but the plant cell has something called a plasma membrane or cell membrane that helps the plant cell absorb water through a process called **osmosis**. The technical definition of osmosis is the whole movement of water across a semi-permeable membrane (in plants, the cell membrane), from an area of lower solute concentration to an area of a higher solute concentration. For example, salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This may be why you can get really thirsty after eating something that is very salty.

Basically, if two solutions of different concentrations are separated by a semi-permeable membrane, the solvent will tend to diffuse through a process called **diffusion,** across the membrane from the less concentrated to the more concentrated solution. This is osmosis and is the process by which plants obtain their water. Osmosis is the nature’s process of obtaining equilibrium (when molecules are equal throughout a space).

Diffusion and Osmosis are both types of **passive transport**, which means that no energy is required for the molecules to move into or out of the cell. Anytime energy is required for movement of molecules across the cell membrane, then it is called **active transport**. The liquids inside and outside of cells have different substances. Sometimes a cell has to work and use some energy to maintain a proper balance of ions and molecules. Salt is easily transferred through the cell membrane and energy is not needed for the osmosis of salt into water. Something like calcium would be diffused into the cell through active transport because it is too large of a molecule to make it through the cell membrane.

Start to think of a plant in terms of a system. There are two main parts to a plant that makes up this system, and these are the roots and the shoots. The roots get the water from the soil that the plant needs to perform its many processes for survival. There are two different systems of roots, the taproot system and the fibrous root system. The taproot system consists of a large central room with a lot of smaller lateral roots coming off of the central root (ex. Think of a carrot or a dandelion root). The fibrous root system is made up of a lot of different roots grouped together that are all about the same size (ex. grass and many flowers have a fibrous root system). **
 * Roots and Shoots:



There is another common part to root systems and that something is called **root hairs**. Root hairs are like little threads that come off of the roots, which increases the surface area of the root altogether. The greater surface area on the root caused by the root hairs allows the plant to absorb more fluids/water.

** The Truth: ** Plants absorb fluids/water with a **fluid transport system**. Since plants do not have a mouth to drink or eat, they have parts like the fluid transport system, which help aid the plant in this process. The fluid/water travels through plants in a set of tubes called ** vascular bundles **, which are a lot like the human and animal circulatory system that transport blood throughout their bodies. These vascular bundles are made of two different kinds of tissues that run along side each other. In each vascular bundle you can find the **Xylem** and the ** Phloem **. Xylem is the tissue where water and dissolved minerals from the soil is transported through the plant. Xylem takes the water up the plant. Phloem is the tissue where the food (glucose) that is produced by a process called photosynthesis. The phloem transfers the glucose down the plant. The plant stores some of the sucrose as starch, as well as the water that it takes in from the xylem in a storage part of the root for safekeeping. People and animals do this same thing as far as storage goes, but instead of storing it in the root, because humans and animals do not have roots, store it in the fat cells of their bodies. Plants and our bodies do this for a number of reasons one of which is growth. Think about how much energy it takes to grow for both humans and plants.
 * A Common Misconception About Roots: ** Plants drink water like people or animals.

Vascular Bundles



The second important part of the plant is the shoot. Shoots are the part of the plant that are above ground, and they are made up of the stem, the leaves, and the flower. The stem and leaves are made of tissues, which are groups of specialized cells that are working together to help the plant thrive. The tissues in the **stem** are xylem and phloem. The **xylem** carries water and minerals throughout the plant and provides the plant with support. **Phloem** carries sugars and other nutrients from the leaves to cells for consumption or storage.

The stem also contains some chlorophyll, which is what makes it green. However, there is a lot more chlorophyll in the leaves. **Leaves** are made up of many tissues and are the part of the plant where photosynthesis and cellular respiration occurs. The surface area to volume is dependent on the environment the plant grows. Most leaves on trees and flowers have a high surface area to volume ratio because it efficiently utilizes the suns energy for the photosynthesis process.They have two outer layers called the epidermis, a mesophyll layer where the chloroplasts are located in between those two layers, **vascular bundles** that are made up of xylem and phloem which carry water and the products of photosynthesis to other parts of the plant, and the stomata that open and close to allow water, air, and solar energy to enter the plant.

**A Common Misconception About Photosynthesis:** Plants make direct use of solar energy for their living processes, without the intermediate process of photosynthesis.
 * The Truth: ** The process of ** photosynthesis **occurs in the mesophyll layer of cells within the leaf between the two epidermis cuticles. The sunlight is taken in through the **stomata** which are located on the epidermis and surrounded by **guard cells** that open and close depending on the needs of the plant. When the sunlight reaches the inside of the leaf, it begins to convert the light into ATP (Adenosine Tri-Phosphate) and NADPH. Then using the chemical energy that is stored in the ATP and NADPH, the hydrogens from water combine with CO2 taken from the stomata to make **glucose**, which is sugar that is sent to every cell of the plant through the xylem and phloem to provide nutrients and energy for things like flower and seed production, growth, and cell maintenance. The tissues in the leaf are also responsible for **cellular** **respiration** . This takes place through the stomata as well. They open to allow CO2 to enter the plant and oxygen to exit. Water also evaporates out of these pores through transpiration. When the stomata sense that the weather is getting hotter, they will open and allow the rate of transpiration to increase so that they plant can get the water it needs more quickly.



= Flowers: =



**A Common Misconception About Flowers:** Flowers are just meant look pretty and smell nice. **The Truth:** Flowers serve a very important role in the lives of plants. The sizes, smell, shape, and pattern of every flower has a certain purpose. The purpose of a **flower** is to draw insects such as bees and butterflies and other pollinators like hummingbirds and bats to the flower. Depending on the pollinator for the specific plant, the shapes of the **pedals** have adapted to better dispense pollen. The scent is also important, not only does it smell good to people, it smells good to pollinators also.

There are many important parts to a flower that help in the pollination and reproduction of the plant. Plants are similar to humans in the fact that there are male and female parts of each flower. Pollen contains the sperm which is the male part that ends up fertilizing the female egg. Pollen is found on the **anther** of a flower which is held up by a stem called a **filament**. These parts together, the anther and the filament make up the **stamen** which is the male part of the flower. The pollen is transferred by pollinators to the **stigma** which is a sticky part that sticks up out of the flower. The stigma is held up by the **style**, the style also is the tube that takes the pollen to the ovary. These three parts; the stigma, style and ovary make up the **carpel** which is the female part of a flower. There are a special kind of petals called **sepals**, they protect the flower before it blooms (see picture below). After the flower completely blooms the sepals become smaller and less noticable. The **ovary** is at the bottom of the flower itself, right before the stem of the flower. The ovary is known by a more common name also; **fruit** ! Fruit is a fleshy covering of the ovule to protect the developing seed. The ovary contains the ovule, and the ovule has the egg in it. This is the pollen’s final destination; but it has a long journey to get there!

Drawing By: Kaitlyn Lund

In flowers, the stamens (male reproductive parts) produce ** pollen grains **. The pollen is carried by wind or insects (pollinators) to the stigma of the carpel (the female reproductive part). It is usually the carpel of a different plant from the one supplying the pollen. Also, it is important to remember that the male and female parts of a plant usually mature at different times to avoid​ self-pollination. The pollen will then germinate and will send a long ** pollen tube ** down the style and into the ovule (what contains the egg cell). This is a very slow process. Two **sperm** remain in the pollen tube until the tube reaches the micropyle (the open end of the embryo sac). The two sperm enter the embryo sac and two ** fertilization ** processes take place. The first sperm fuses with the egg and forms an embryo. The other sperm fuses with two polar nuclei which creates an endosperm (the nutritive tissue of the future seed). In the ovule, tissues develop in the seed coat. When this new plant matures, the raw seed is ready to separate from the plant and start the next generation. It is a never-ending cycle! (Violet Snow, 2007).





A plant will use ** seed dispersal **to continue this cycle and spread its species. Some plants, like the Dandelion, rely on the wind to bring their seeds to environments that are favorable for growth. Others, like the watermelon, rely on animals either to carry the seeds away or to have the animals eat the fruit containing the seed, thus allowing the seed to pass through the animal's digestive track. This seed, once dispersed, starts off as a dormant embryo encased in a protective outer shell called a ** seed coat ** which sheds once the seed senses certain cues that tell it when it's a good time to begin germination. This includes enough water, oxygen, and an appropriate temperature. A **cotyledon** is a significant part of this embryo. During germination, it may become the first leaves of a seedling. Also, the number of cotyledons determines the classification of many flowering plants. “Monocots” are plants with one cotyledon while “dicots” are those with two. Some cotyledons may even be photosynthetic, so they are often times confused with leaves. But true leaves and cotyledons are developmentally different. Cotyledons are formed during embryogenesis, so they are present before germination occurs. They are usually meant to store the food reserves – the **endosperm** – of the seed until they are used up and the cotyledons are not needed anymore. Leaves, however, are formed afterward. As a plant embryo grows, the **hypocotyl** emerges and lifts the growing tip above the ground including the embryonic leaves and the beginnings of the first true leaves. It is the primary organ of extension of a young plant that grows into the stem.

Drawing by: Kaitlyn Lund

Environmental Responses: **A Common Misconception About Hormones:** Only animals and humans have hormones. **The Truth: Most of the time we think that animals and humans are the only living things that have hormones, but plants do as well. ** **Hormones are chemical messengers and substances, which when they are releases into a particular part of an organisms that stimulate physiological action in a different part of the plant. Hormones role in both animals and plants, is to regulate the growth and development as well as assimilate functioning of all the parts of the plant. Basically, hormones help plant buds grow, the leaves to fall off, and for the ripening of fruit. Hormones help plants to respond to whatever happens in their environments be it an animals eating their leaves or hungry bugs. ** For animals, hormones come from glands but in plants, hormone production comes from the collections of cells in the plant that carry out the needed functions. There is one very important hormone that is found in plants called **ethylene. Ethylene is a gaseous hormone that is usually associated with fruit ripening in plants. The functions of ethylene are: **


 * Stimulates the release of dormancy.
 * Stimulates shoot and root growth and differentiation (something also called triple response
 * May have a role in adventitious root formation.
 * Stimulates leaf and fruit detachment.
 * Stimulates flower opening.
 * Stimulates flower and leaf deterioration.
 * Stimulates fruit ripening.

Today, we use ethylene to help accelerate fruit ripening in produce. An experiment you can try on your own is to take a very ripe banana and stick it next to an unripe banana. You will find that the unripe banana will ripen very quickly, and this is due to the hormone ethylene.

Plants have another member of the hormone family that helps with photosynthesis; this hormone is called **auxin. Auxin, also known as IAA, is the reason that Christmas trees have an “A” shape. Auxin is located in the shoot and roots, and is transported throughout the plant. Plants use the suns energy for photosynthesis but what happens when the plant is unable to get the most direct amount of sunlight for efficient photosynthesis. The way that evolution has aided plants to maximize energy consumption is the ability to follow the direction of the sun, a process called phototropism. ** It is able to do this by a process called elongation by using the auxin cells located throughout the plant. The shoots curve in the response to the light. When the light from the sun or some cases lamps hit one side of the plant, the IAA begins to move to the other side of the plant, where IAA aides in the elongation of cells on the far side. This effect is for the shoot to curve towards the light.

Plants have an amazing ability to sense which way is up and which way is down. They response to the earth’s natural gravity to turn or grow, and this ability’s name is **gravitropism. When a seed is initially sprouting, the roots and the shoots need to go in a specific direction, that being up and down. ** An experiment you can try to see the effects of gravitropism by placing a potted plant on its side. You should observe that the plant will begin to elongate so that the shoots are pointed in the direction of the suns light.



Now that we know about how plants can bend toward the direction of light and adapt to gravity, we can learn about plants response to seasonal change. You may have noticed that the leaves on trees will become brightly colored during the fall season and eventually fall off. Trees that display this seasonal loss of leaves are called **deciduous trees. The trees cannot efficiently make food through photosynthesis during the winter season because the temperature is too low and the suns light is often blocked. The energy that the tree would need to generate would be exponential. Much like bears hibernate during the winter, trees go into dormancy where there is a low level of metabolic activity (energy consumption and production). **

So how is it that these seasonal deciduous trees are able to detect the approach of winter? There are generally two factors, the first being the low temperature change and the other is an occurrence called **photoperiodism. Some may confuse phototropism and photoperiodism but the difference is on phototropism the plant is bending toward the light and photoperiodism is the effect where plants make seasonal adaptations in regard to the length of the nights they are experiencing. Photoperiodic flowering plants are classified in two groups: long-day plants or short-day plants, but the controlling mechanism is actually managed by the hours of darkness, and not the length of the daylight. Some short-day plants are coffee, strawberry, tobacco, cotton, rice and sugar cane. Some long-day plants are the pea, barley, lettuce, wheat, turnip, carnations, oat, and clover (Krough 2002). **

Belk, Colleen. Maier, Virginia B (2010). "Biology: Science for Life." Pearson Education, Inc: San Francisco, CA.
 * Bibliography: **

Chiras, Daniel (1993). "Biology: The Web of Life." West Publishing Company: St. Paul, MN.

CliffsNotes.com. Energy Regulators: Enzymes and ATP. 4 Oct 2009 < []>.

Krogh, David. Biology: A Guide to the Natural World. Second Edition. Upper Saddle River, NJ: Prentice Hall, 2002. Print.

Snow, Violet (2007). "Seeds to Flowers to Seeds: Reproduction in Flowering Plants." Suite101.com. Retrieved October 2, 2009 from Web Site: [].

Purves, William. //Life: The Science of Biology //. 6th ed. Sunderland, Massachusetts: Sinauer Associates, Inc., 2001. Print.