Plant Structures

Once students understand how organisms obtain energy to survive, they focus on plants and how plants have specific structures that allow them to access what they need to survive. Specifically, they analyze how temperature affects the transpiration rate in plants.  

• The external structures of living things, such as plants, help them get what they need to survive. Structure refers to the way in which parts are put together to form a whole.  
• Leaves have structures called stomata, which are pores that open and close. Stomata exchange gasses with the environment. When the plant’s stomata are open, some water evaporates back into the environment. This process is called transpiration.
• A system is a set of connected, interacting parts that form a more complex whole. The plant is made up of interacting parts that work together to support the functioning of the entire plant.
  
  

• How are a plant’s structures related to the plant’s ability to function?
• Why is a plant considered a system?
• How do roots help a plant survive? How does the stem help a plant survive?
• Why is it important that the stomata open and close?
• Why do plants need carbon dioxide?
• What else do plants need to photosynthesize, in addition to sunlight and carbon dioxide?  
• How do plants cycle water back into the environment?
• How do the plant’s structures work together to make transpiration happen?  
• Why is transpiration affected by temperature?  
• How do leaves help a plant survive?
  
  

Misconception: The organisms in an ecosystem are not part of a larger whole, but instead are just a collection of living things surviving independently of one another and their environment.

Fact: Ecosystems are systems, made up of smaller interacting parts. Both the living and nonliving parts of an ecosystem influence the overall ecosystem.

Misconception: An organism is not a system.

Fact: All organisms are systems because they are made up of smaller structures that have a specific function and work together to help the organism survive.

Function:  the normal action of something or how something works

Life Cycle:  the series of developmental stages an organism passes through on its way from birth to death

Photosynthesis:  the process of turning sunlight, carbon dioxide, and water into glucose and oxygen

Plant: a living thing that captures energy from sunlight for growth and development

Reproduction: the ability of a mature organism to have offspring

Structure: the way in which parts are put together to form a whole

Transpiration: the evaporation of water from plant leaves

A Plant’s Structures

All plants have roots. The roots help to anchor the plant against the forces of wind and moving water. The roots also keep the plant upright and balanced. They also gather water and nutrients and transport them to the rest of the plant.

The stem supports the leaves, fruits, and flowers. It also transports water and nutrients between the roots and the rest of the plant. The stem also absorbs some water, although not as much as the roots.

The leaves have the most chloroplasts, to help create food for the plant through photosynthesis.

Transpiration

Leaves also have structures that allow them to take in carbon dioxide from the environment and release oxygen. Plants are constantly exchanging gasses, in the same way that people are always breathing. To do this, they have pores called stomata that open and close to take in the gasses.

When the stomata are open, some water evaporates back into the environment through transpiration. After plants absorb precipitation from the ground through their roots and the stem carries it to the leaves, some of the water evaporates back to the atmosphere. This is why transpiration is part of the water cycle.

The amount of water that a plant transpires depends on several factors. Light, heat, humidity, and wind all affect how much a plant will transpire.

For example, when it is really hot, plants often pull in a lot of water through their roots and release it into the atmosphere. They do this to try to cool off.

The type of soil the plant is growing in also affects transpiration. For example, plants that live in dry soils might close their stomata during the hottest time of the day. They do this to try to keep that moisture so they don’t dry out too much.

In the wetlands, there is plenty of water, so plants continue to transpire during the hot times of the day.

This is why the small pool of water in the Nebraska wetlands would dry up every afternoon. Some of the water evaporated into the atmosphere, and the rest of it was transpired by the plants. During the nighttime, temperatures cooled off, and so transpiration slowed down. This allowed the pool to refill with groundwater.

In this lesson, students conduct an investigation that compares the water loss of plants with leaves when exposed to warm temperatures and cool temperatures. Students record the initial mass of the plant water before it is placed in each experimental condition and then measure the final mass of the plant’s water after 24 hours to calculate the total mass of water lost in each separate condition.