This biology worksheet breaks down the components of DNA, helping students visualize nucleotides and understand base pairing rules.

It looks like you've uploaded an image of a worksheet titled "Karyn Division", which appears to be about DNA structure and base pairing. The task involves labeling parts of a DNA molecule and understanding hydrogen bonding between nitrogenous bases.

Let’s go through the problem step by step and solve it based on what's visible in the image.

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🔬 Understanding the Image:

The diagram shows a segment of a DNA double helix with labeled components:

- Sugar
- Phosphate
- Nitrogen base
- Hydrogen bond
- Base pair

There are two strands, each made up of repeating units of:
- Phosphate group
- Deoxyribose sugar
- Nitrogenous base

The bases are paired across the two strands via hydrogen bonds.

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✔ Task 1: Labeling the Diagram

From the image, the following labels are already provided or need to be completed:

1. Sugar: Likely deoxyribose (since this is DNA).
2. Phosphate: Part of the sugar-phosphate backbone.
3. Nitrogen base: The nitrogen-containing molecules that pair across strands.
4. Hydrogen bond: Lines connecting complementary bases.
5. Base pair: A pair of nitrogenous bases connected by hydrogen bonds.

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🧬 Base Pairing Rules:

In DNA:
- Adenine (A) pairs with Thymine (T) → forms 2 hydrogen bonds
- Guanine (G) pairs with Cytosine (C) → forms 3 hydrogen bonds

This is critical for answering questions about base pairing and hydrogen bonds.

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❓ Questions from the Worksheet:

Let’s analyze the multiple-choice questions at the bottom (as seen in the image):

> Which of the following best describes the relationship between adenine and thymine?
>
> A) They are both purines
> B) They are both pyrimidines
> C) They form three hydrogen bonds
> D) They form two hydrogen bonds

✔ Correct Answer: D) They form two hydrogen bonds

- Adenine and thymine are not both purines or pyrimidines — adenine is a purine, thymine is a pyrimidine.
- They form two hydrogen bonds, not three.
- Guanine and cytosine form three hydrogen bonds.

So, D is correct.

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> Which of the following statements is true about the sugar in DNA?
>
> A) It is ribose
> B) It is deoxyribose
> C) It has an extra oxygen atom
> D) It is found in RNA

✔ Correct Answer: B) It is deoxyribose

- DNA contains deoxyribose sugar (lacks an oxygen at the 2' carbon).
- RNA has ribose, which has a hydroxyl (-OH) group at the 2' position.
- So, B is correct.

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> How many hydrogen bonds are formed between guanine and cytosine?
>
> A) 1
> B) 2
> C) 3
> D) 4

✔ Correct Answer: C) 3

- G-C base pairs have three hydrogen bonds.
- This makes them stronger than A-T pairs.

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> What holds the two strands of DNA together?
>
> A) Covalent bonds
> B) Ionic bonds
> C) Hydrogen bonds
> D) Van der Waals forces

✔ Correct Answer: C) Hydrogen bonds

- The hydrogen bonds between complementary nitrogenous bases hold the two strands together.
- Covalent bonds are within each strand (sugar-phosphate backbone).

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🧠 Summary of Key Concepts:

| Concept | Explanation |
|--------|-------------|
| Sugar in DNA | Deoxyribose (no -OH at 2') |
| Bases | A, T, G, C |
| Base Pairing | A-T (2 H-bonds), G-C (3 H-bonds) |
| Backbone | Sugar + Phosphate (covalent bonds) |
| Strand Connection | Hydrogen bonds between bases |

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✔ Final Answers:

1. Adenine-Thymine pairing: D) They form two hydrogen bonds
2. Sugar in DNA: B) It is deoxyribose
3. Hydrogen bonds between G and C: C) 3
4. Holds strands together: C) Hydrogen bonds

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If you'd like me to explain any part in more detail (e.g., how to draw DNA, why base pairing matters, etc.), feel free to ask!