“Seeing” Photosynthesis

“Seeing” Photosynthesis Subtitle: Visualizing the Process, Step by Step

Table of Contents • Photosynthesis Overview • Q&A: Check Your Understanding Slide 3 • Video: Common Misconceptions Slide 3 • Video: Overview & Science History Slide 4 • Photosynthesis: Step by Step Slide 5 • Leaves & Leaf Anatomy Slide 13 • Video: Travel Deep Inside a Leaf Slide 16 • Respiration & The Carbon Cycle Slide 17 • The Chemistry of Photosynthesis Slide 20 • Extension Video: The Calvin Cycle Slide 25 • Extension: Children’s Science Book Project Slide 26

Photosynthesis: Check Your Understanding • How do plants get food? • How do they get the energy to grow? • How do trees help us breathe? • Where do trees get their mass from? (Pretend you’re holding a branch in your hand. Where did that weight come from?) Watch this video about common misconceptions. Many adults — even MIT graduates! — struggle to understand the science. Veritasium Video: “Where do trees get their mass from?” • https://www.youtube.com/watch?v=2KZb2_vcNTg • Video (4.09 mins)

Photosynthesis: Optional Overview • NOVA: Earth | Photosynthesis Video (2.25 min) • An exploration of the history of plant biology — from the earliest scientific hypotheses that plants ate dirt, to our present-day understanding of photosynthesis. • https://www.pbslearningmedia.org/resource/tdc02.sci.life.stru.photosynth/photosynthesis/#.WsgMrNPwb-Z

How do plants make their own food? • Through a chemical process called photosynthesis. • Plants need three components to make their own food: • Water (from the soil) • Carbon Dioxide (from the air) • Energy (from sunlight)

Photosynthesis: The Products Photosynthesis produces two main things: • Glucose (sugars) • Oxygen light energy carbon dioxide + water glucose + oxygen

Photosynthesis: Step by Step • Water: The plant sucks up water from the ground. Water is collected through the roots, travels up through the stem and into the leaves. • Carbon Dioxide: This gas gets into the leaves through tiny openings called stomata in the outer layer of the leaf.

Photosynthesis: Step by Step • Sunlight: Energy from sunlight is captured by special compartments called chloroplasts in the leaves. • Chloroplasts contain chlorophyll, which absorbs light energy from the sun.

Photosynthesis: Step by Step • Next is a step that people often miss: • The sunlight energy splits the water molecules into hydrogen (H) and oxygen (O2). • Where do the molecules go from there?

Photosynthesis: Step by Step • After the water molecules are split, the carbon atoms in CO2 hook up with the hydrogen (H) atoms to form a new molecule called glucose (sugars). This is the plant’s food! • What happens to the oxygen after the split?

Photosynthesis: Step by Step • The oxygen is released into the air through the stomata of the leaf — along with water vapor. • A stoma (plural: stomata) is a tiny hole used for gas exchange.

The Big Picture Optional Assignment: Explain the Process • Draw, verbally describe, or act out the photosynthesis process, stepby step, as a class.

Leaves Up Close Q: Where does photosynthesis happen? A: In the leaves of green plants. Here’s a close-up of a plant cell. Can you see the stomata? Where are they located?

Cross-Section of a Leaf • Epidermis: The outer layer of the leaf. It protects the cells inside, but allows sunlight to reach the chloroplasts. • Stoma: A tiny hole in the epidermis of the leaf. These are used for gas exchange — to bring in the carbon dioxide needed for photosynthesis, and to expel oxygen and water vapor. • Chloroplast: The key player! This is where photosynthesisoccurs. Chloroplasts contain chlorophyll.

Chloroplast Close-Up • Chloroplasts: The part of the leaf where photosynthesis occurs. They contain chlorophyll as well as other tiny structures that aid in photosynthesis. • Chlorophyll: The thing that makes the photosynthesis reaction possible! It captures the light energy, stores it, and uses it to spur on the reaction. It also has a green pigment, which gives plants their green color.

Living, Breathing Leaves • Travel Deep Inside a Leaf | California Academy of Sciences • https://www.youtube.com/watch?v=pwymX2LxnQs • This fascinating video takes us on a journey inside a leaf of a redwood tree. Enter the stoma and view photosynthesis on a molecular level. PAUSE POINT Suggested sequence: Fill out Part 1 of the Student Worksheet: “Zooming In on Leaf Structure” after watching this video. Conduct the Floating Leaf Disk Experiment and complete Part 2 of the Student Worksheet. Resume PowerPoint presentation.

Cellular Respiration: Part 1 • What is cellular respiration? It’s how plants and animals break down glucose (made from photosynthesis) and turn it into energy. • When we eat plants, or eat an animal that has eaten plants, that food goes through the respiration process to break it down. • We eat food (containing glucose) and breathe in oxygen. • What happens next?

Cellular Respiration: Part 2 • The glucose and oxygen go through their own chemical eaction, which produces energy — the same energy stored by the plant through photosynthesis! • Besides energy, the reaction also produces water and carbondioxide. When we exhale we get rid of that carbon dioxide and water — which is later taken in by plants… and the cycle continues over and over.

The Big Picture Think about the huge tree you saw in the first video. Where did it get its biomass? How does photosynthesis fit into the big picture? How is it related to respiration and the carbon cycle? Look at the ocean here. Like land plants, phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy. They consume carbon dioxide and release oxygen.

Sunlight: The Ultimate Energy Source • What’s for lunch today? Follow the food chain. • Photosynthesis is the basis for essentially all food chains. Because all life starts with the sun — from phytoplankton on up!

Global Distribution of Photosynthesis • Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.

The Chemistry of Photosynthesis • As you’ve learned, photosynthesis produces not only glucose, but also waste in the form of oxygen gas (O2) and water vapor (H2O). The overall chemical equation for photosynthesis looks like this: • 6 CO2 + 12 H2O + (Light Energy)C6H12O6 + 6 O2 + 6 H2O Spelled out in words, this means: Carbon dioxide + water + (energy from sunlight)  glucose + oxygen + water vapor

The Chemistry of Respiration • When humans or other animals eat a plant, we process the glucose as food for our own energy and growth. The glucose, along with the molecules of oxygen gas we breathe in from the atmosphere, undergo a chemical reaction of their own. • Like photosynthesis, cellular respiration creates waste in the form of carbon dioxide and water, which we exhale out of our lungs. The reaction looks like this: C6H12O6 + 6 O2 (Energy) + 6 CO2 + 6 H2O Spelled out in words, this means: Glucose + oxygen  (energy) + carbon dioxide + water vapor

Photosynthesis vs. Respiration Photosynthesis 6 CO2 + 12 H2O + (Energy)C6H12O6 + 6 O2 + 6 H2O Respiration C6H12O6 + 6 O2(Energy) + 6 CO2 + 6 H2O • What do you notice about these two equations? • Plants and animals have been recycling each other’s molecules for millions and millions of years!

Extension: Photosynthesis, Part 2 • Calvin Cycle Video • Nature’s Smallest Factory: The Calvin Cycle • https://www.youtube.com/watch?v=0UzMaoaXKaM&t=236s • Learn about the second phase of photosynthesis — called the Calvin Cycle — which converts carbon dioxide into sugar with some clever mix-and-match math.

“Seeing” Photosynthesis