Egg-speriment with cell

Art in Motion: Plant Tropisms Text Version

The silhouettes of four seedlings, arranged by increasing height, are shown.

Text reads Phototropism: Response to Light.

The seedlings grow upward slowly toward the light source. However, once the light source moves to the far left, the seedlings bend to the left and continue to grow toward the light.

Next, the silhouette of a seedling protruding horizontally from a bulb is shown.

Text reads Gravitropism: Response to Gravity.

The seedling grows horizontally out of the bulb but then starts to bend and grow downward.

Next, a thin vine is shown in front of a tree trunk.

Text reads Thigmotropism: Response to Touch.

The vine touches the tree trunk and then slowly grows around it in a corkscrew motion. The vine is then shown wrapping itself around one of the tree’s upper branches.

Art in Motion: Plant Tropisms Text Version

The silhouettes of four seedlings, arranged by increasing height, are shown.

Text reads: Phototropism: Response to Light.

The seedlings grow upward slowly toward the light source. However, once the light source moves to the far left, the seedlings bend to the left and continue to grow toward the light.

Next, the silhouette of a seedling protruding horizontally from a bulb is shown.

Text reads: Gravitropism: Response to Gravity.

The seedling grows horizontally out of the bulb but then starts to bend and grow downward.

Next, a thin vine is shown in front of a tree trunk.

Text reads: Thigmotropism: Response to Touch.

The vine touches the tree trunk and then slowly grows around it in a corkscrew motion. The vine is then shown wrapping itself around one of the tree’s upper branches.

Most cells contain the same compounds. The graph compares the percentages of some compounds found in a bacterial cell and in an animal cell.

There are only two main types of cells; however, they are very different. They are called eukaryotic cells and prokaryotic cells. These two cell types make up all life. An organism can be made of either eukaryotic or prokaryotic cells, but not both.

Most organisms are made of eukaryotic cells, including you! The cells of protists, fungi, plants, and animals, including humans, are all eukaryotic cells. An organism that is composed of eukaryotic cells is called a eukaryote. Eukaryote is pronounced eu-kary-ote. It is easy to remember that this is the type of cell that makes up your body because the word eukaryote begins with the letters eu-, which sounds like the word “you.” They make up you! Eukaryotes can be made of one cell, like an amoeba, but most are made of trillions of cells, like an elephant. Eukaryotic cells are much more complex than prokaryotic cells because they contain their DNA in an enclosed nucleus. A nucleus is a structure in the cell that contains the DNA of the cell. Think of the nucleus as an envelope that encloses a letter, but instead of a letter, the nucleus encloses DNA. DNA is the set of genetic instructions that tells the cell what to do. Eukaryotic cells also have a cell membrane, or protective outer layer, that keeps the inside of the cell together, much like how an inflated balloon keeps the air inside from escaping. Eukaryotic cells have more organelles, or cell parts, and are much larger than prokaryotic cells.

Prokaryotic cells are much simpler than eukaryotic cells and existed on Earth long before eukaryotic cells. Organisms made out of prokaryotic cells are called prokaryotes. Almost all prokaryotes are single-celled organisms. Prokaryotic cells are the smallest form of life that can live independently. Bacteria is the most common prokaryote; however, there are other prokaryotic cells called archaea. Prokaryotes do not have a nucleus. Their DNA, or genetic instructions, simply floats inside the cell in a single strand. Like eukaryotic cells, prokaryotic cells also have a protective cell membrane.

As you have learned, most organisms are made of multiple eukaryotic cells. Eukaryotic cells are complex cells that contain DNA in a nucleus. Organisms with prokaryotic cells are usually single-celled, have no nucleus, and their DNA floats around inside the cell. Eukaryotic cells and prokaryotic cells do share some characteristics in that they both have cell membranes and contain DNA. Organisms can either be made of prokaryotic or eukaryotic cells, but not both.

Art in Motion: Passive and Active Transport Text Version

In order to live and function, cells must let certain materials enter and leave. The cell membrane controls how materials move into or out of a cell.

An illustration displays a cross-section of a cell membrane. Within the body of the cell membrane are two structures: a protein channel, which is a narrow opening in the membrane, and a transport protein, which is open on one side of the membrane and closed on the other side. Groups of different types of molecules float on both sides of the cell membrane.

The cell membrane is selectively permeable, which means that some substances can pass through the membrane, while others cannot.

A large, irregular shape floats toward the cell membrane, bounces off, and floats away.

Substances move into or out of a cell by one of two processes: passive transport or active transport.
Passive Transport

The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport. In passive transport, molecules are able to pass through the cell membrane in both directions.

Molecules labeled “sugar,” “water,” and “oxygen” pass back and forth across the cell membrane, moving into and out of the cell.

When there are more molecules in one area, materials will gradually move from an area of higher concentration to an area of lower concentration.

The groups of molecules labeled “sugar,” “water,” and “oxygen” are highlighted. An arrow points from the oxygen group inside the cell, which is larger, to the oxygen group outside the cell, which is smaller. Another arrow points from the large group of water molecules outside the cell to the smaller group inside the cell. Water and oxygen molecules drift from their smaller to their larger groups, passing through the cell membrane.

Diffusion is one type of passive transport.
Diffusion

Small molecules, like oxygen, move into or out of the cell by passing through the cell membrane.

The path of the drifting oxygen molecules, which are the smallest molecules present, is highlighted. These molecules pass directly through the cell membrane.

Osmosis is another type of passive transport.
Osmosis

Water molecules diffuse into or out of the cell by traveling directly through the cell membrane.

The path of the drifting water molecules, which passes directly through the cell membrane, is highlighted.

Facilitated diffusion is a third type of passive transport.
Facilitated Diffusion

Molecules that cannot pass directly through the cell membrane, like sugar, move through protein channels in the cell membrane.

The path of the sugar molecules, which are larger than the oxygen or water molecules, is highlighted. These molecules pass into and out of the cell through the opening labeled as the protein channel.

Passive transport maintains balance inside the cell.
Active Transport

The movement of materials through the cell membrane using cellular energy is called active transport.

The illustration focuses on the structure labeled as the transport protein. Inside the cell are molecules labeled “calcium.” Outside the cell are more calcium molecules. There is an opening on the end of the transport protein that is outside the cell.

Energy is needed to move molecules from a place of lower concentration to a place of higher concentration.

The calcium molecules on both side of the cell membrane are highlighted. There are eight molecules inside the cell and three molecules outside the cell. An arrow points through the transport protein from the outside to the inside of the cell.

Proteins in the cell membrane “pick up” specific molecules, like calcium. Using energy from the cell, the transport protein carries the molecule across the membrane and releases the molecule on the other side.

One of the calcium molecules outside the cell enters the open end of the transport protein and is pulled to its center. A burst labeled “Energy” appears briefly inside the cell, and the inside end of the transport protein opens while the outside closes. The calcium molecule moves from the center of the transport protein toward its opened end and is released inside the cell. This process repeats with another of the calcium molecules outside the cell.

The illustration returns to an overview of the cell membrane with both the protein channel and the transport protein visible. Sugar, water, oxygen, and calcium molecules float around the cell membrane. The transport protein opens and closes with bursts of energy as calcium molecules pass through.

Materials are constantly entering and leaving the cell through passive and active transport.

Inquiry Warm-Up: Will Mosses Absorb Water? Answer Key

Students should observe that peat moss absorbs water well, and it absorbs water better than sand does.
Mosses need to absorb water and nutrients from their environment for survival and reproduction. Without vessels to transport it, water would be unable to reach parts of the plant if those parts could not absorb and retain it themselves.
One purpose of adding peat moss to the soil is to hold moisture in the soil while new plants become established.