Crunch Time (week of 7-11 April)

Bella and Nathan are studying the biological levels of organization, which range from a single cell all the way up to the biosphere in a highly structured hierarchy. The biological hierarchy includes: cells, tissues, organs, organ systems, and organisms. Consider each of the pairs shown below. Select ALL that correctly pair the level with an appropriate example.

• organ: heart

• cell: neuron

• tissue: blood

• organ: muscle

• organ system: small & large intestines, stomach, pancreas, liver, gall bladder

Answer explanation

The correct pairs are: organ: heart (heart is an organ), cell: neuron (neuron is a type of cell), tissue: blood (blood is a tissue), and organ system: small & large intestines, stomach, pancreas, liver, gall bladder (these are part of the digestive system).

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Hierarchical Organization

During a biology class, Sophia was asked to identify components of blood tissue. All of these make up blood tissue, except:

• A) platelets

• B) red blood cells

• C) white blood cells

• D) smooth muscle cells

Answer explanation

Smooth muscle cells are not components of blood tissue. Blood is made up of platelets, red blood cells, and white blood cells, which are all essential for its functions.

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Hierarchical Organization

By the late 1600s, scientists began using a new tool, the microscope. Their observations proved the existence of a whole new world of microorganisms and helped to establish the tenets of the Cell Theory, including that life is made of cells. However, most still held that these microorganisms arose spontaneously from a “vital force.” In the late 1700s, Lazzaro Spallanzani designed an experiment to show that life did not arise spontaneously from food. He inferred that some foods spoil because of growing populations of microorganisms. Spallanzani boiled meat broth in open flasks. He sealed the flasks of the experimental group which showed no signs of microbe growth. Critics of Spallanzani said that he only showed that organisms cannot live without air.

In 1859, Louis Pasteur designed an experiment to address the spontaneous generation. He used a curved-neck flask that allowed the air inside the flask to mix with air outside the flask, but prevented solid particles, like microorganisms, from entering the body of the flask. Compare and contrast the work of Pasteur and Spallanzani and explain how both men influenced the cell theory.

• A) They proved that cells cause disease.

• B) They proved that boiling kills microorganisms.

• They proved that plants, animals, fungi, protists, and bacteria are all made of cells.

• They proved that cells do not appear spontaneously, but only come from pre-existing cells.

Answer explanation

Both Spallanzani and Pasteur demonstrated that life does not arise spontaneously, supporting the idea that cells come from pre-existing cells. Their experiments refuted spontaneous generation, a key aspect of cell theory.

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Cell Theory

Elenciah and Austin are working on a science project where they build an electromagnet by wrapping a wire around a nail and connecting the wire to both terminals of a battery. When they test the electromagnet, it can pick up 6 paper clips. Their teacher wants all groups to pick up at least 10 paper clips. What revisions could Renaldo and Nasreen make to increase the number of paper clips their electromagnet picks up?

• make the wire longer

• remove the nail from the center of the wire

• increase the number of loops of wire around the nail

• spread the loops of wire apart on the nail so they do not touch

Answer explanation

Increasing the number of loops of wire around the nail enhances the magnetic field strength, allowing the electromagnet to pick up more paper clips. More loops create a stronger magnet, which is essential for meeting the teacher's requirement.

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Types of Forces

Jose pushes a 2-kg box with a force of 10-newtons. The box slides across the floor at a constant speed of 5 m/s. What is a valid conclusion from this situation?

• The force of friction was 10-newtons.

• The 10-newton force was an unbalanced force.

• There was not friction experienced by the box.

• There is a net force of 10-newtons on the box.

Answer explanation

Since the box moves at a constant speed, the applied force of 10-newtons is balanced by the force of friction. Therefore, the force of friction must also be 10-newtons, making this the correct conclusion.

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Unbalanced Forces

Label the levels of organization in the correct order.

a

b

c

d

e

organ

tissue

cell

organ system

organism

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Hierarchical Organization

Ethan is studying biology and learns that a group of tissues is a . . . (a)  

• organ

• cell

• tissue

• system

Answer explanation

A group of tissues forms an organ, which is a structure composed of different types of tissues working together to perform specific functions. Therefore, the correct answer is 'organ'.

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Hierarchical Organization

Jaylen noticed that when he painted his room, the color of the walls changed from white to blue. This change in color is an example of:

• Chemical Change

• Physical Change

• Positive Change

• Negative Change

Answer explanation

The change in wall color from white to blue is a physical change because it involves a change in appearance without altering the chemical composition of the paint or the walls.

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Physical and Chemical Changes

Sophia and Matthew are playing with a ball in the park. Which of the following best explains why the ball stops rolling on the flat grass surface?

• The ball's weight causes it to stop.

• Gravity pulls the ball to a stop.

• Friction between the ball and the grass slows it down.

• The ball loses energy as it rolls.

Answer explanation

The ball stops rolling due to friction between the ball and the grass, which slows it down. While gravity and energy loss play roles, friction is the primary reason for the ball's deceleration on the grass.